Manual TABLE OF CONTENTS Module 3.

TABLE OF CONTENTS

MODULE 3. SURVEILLANCE
TABLE OF CONTENTS

3.1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5

MODULE OBJECTIVES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5
MODULE SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6

3.2 DESIGN PROCESS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6

PROBLEM IDENTIFICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
Identify and Locate Operational Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
Determine Functions of Surveillance System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7
Type of Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8
Traffic Measures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8
Real-Time and Historical Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9
Importance of Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9
Inventory Existing Surveillance Capabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10
IDENTIFICATION OF PARTNERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10
Intra-agency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10
Interagency (Information Exchange) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-11
Additional Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-12
ESTABLISH GOALS AND OBJECTIVES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-12
ESTABLISH PERFORMANCE CRITERIA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13
DEFINE FUNCTIONAL REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13
DEFINE FUNCTIONAL RELATIONSHIPS, DATA REQUIREMENTS, AND
INFORMATION FLOWS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14
IDENTIFY AND SCREEN TECHNOLOGIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-15
Identify Alternative Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-15
Evaluate Alternative Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-16
Select Appropriate Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-16
PLAN DEVELOPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-17
Design Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-17
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-17
IDENTIFY FUNDING SOURCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-17
IMPLEMENTATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-19
EVALUATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-19
Monitoring Traffic Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-20
Detecting Incidents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-20
Implementing Control Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-20
Monitoring Environmental Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-21

3.3 TECHNIQUES AND TECHNOLOGIES . . . . . . . . . . . . . . . . . . . 3-21

SYSTEM COMPONENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-21
Detection Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-22
Hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-24

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Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-25
Incident Detection Algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-25
Real-Time Expert Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-25
Communications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-26
SURVEILLANCE TECHNOLOGIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-27
EMBEDDED DETECTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-27
Inductive Loop Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-28
Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-28
Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-28
Installation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-32
Magnetometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-34
Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-34
Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-34
Installation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-34
NON-INTRUSIVE DETECTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-35
Microwave Radar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-37
Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-37
Continuous Wave. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-37
Frequency Modulated Continuous Wave (FMCW) . . . . . . . . . . . . . . . . . 3-37
Pulsing Waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-37
Wide Beam. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-38
Narrow Beam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-38
Long-Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-38
Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-39
Installation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-39
Infrared . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-40
Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-40
Active. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-40
Passive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-40
Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-40
Active . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-40
Passive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-42
Installation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-42
Ultrasonic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-44
Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-44
Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-44
Installation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-45
Acoustic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-45
Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-45
Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-45
Installation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-45
Video Image Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-47
Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-47
Classes of VIP Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-47
VIP Detector Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-48
Advantages of VIP Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-49
CCTV Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-50

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Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-50
Installation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-51
COMPARISON OF EMBEDDED AND NON-INTRUSIVE DETECTORS . . . . . . 3-51
VEHICLE PROBES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-51
Types of Vehicle Probes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-53
Automatic Vehicle Identification (AVI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-53
Active . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-53
Passive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-54
Semi-Active . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-54
Type I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-54
Type II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-54
Type III . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-54
Automatic Vehicle Location (AVL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-54
Dead-Reckoning and Map-Matching . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-55
Signpost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-55
Ground-Based Radio-Navigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-55
LORAN-C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-56
Global Positioning System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-56
Differential GPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-56
Cellular Telephones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-56
MOBILE REPORTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-57
Cellular Telephones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-57
Freeway Service Patrols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-58
Call Boxes/Emergency Telephones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-58
CLOSED-CIRCUIT TELEVISION (CCTV) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-58
Fixed Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-59
Full Motion Video . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-60
Compressed Video . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-60
Portable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-61
SUMMARY OF TRAFFIC SURVEILLANCE APPLICATIONS . . . . . . . . . . . . . . 3-61
ENVIRONMENTAL DETECTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-62
Freeways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-62
Tunnels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-65

3.4 LESSONS LEARNED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-65

OPERATIONS AND MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-65
Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-65
Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-66
Operations and Maintenance Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-66
PRIVACY CONCERNS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-67
SPACING AND PLACEMENT ISSUES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-70
Mainline Traffic Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-70
Spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-70
Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-70
Non-Intrusive Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-71
CCTV Cameras . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-71

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Site Selection Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-71

Preliminary Site Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-72
Final Site Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-72

3.5 EXAMPLES ................................................. 3-73

MIAMI AUTOMATIC VEHICLE LOCATION (AVL) . . . . . . . . . . . . . . . . . . . . . 3-73
TRANSCOM ELECTRONIC TOLL AND TRAFFIC
MANAGEMENT (ETTM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-74
HOUSTON AUTOMATIC VEHICLE IDENTIFICATION (AVI) . . . . . . . . . . . . . 3-75
CONNECTICUT MICROWAVE RADAR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-75

3.6 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-77

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MODULE 3. SURVEILLANCE

Figure 3-1. Closed-Circuit Television Camera.

3.1 INTRODUCTION words, the goals and objectives of a

surveillance system should be defined first,
In a traffic management system, the and then the system should be designed to
surveillance component is the process in meet these goals and objectives. A common
which data is collected in the field. This data mistake to be avoided is to first install a
is used to supply information about surveillance system, then ask the question
conditions in the field to other system “What can this system do for me?”. It is
components. Surveillance provides the essential to determine what system elements
information needed to perform the following are to be supported before selecting and
functions: designing a surveillance system.

C Measure traffic and environmental MODULE OBJECTIVES

conditions.
The objectives of this module are as follows:
C Make control decisions.
C Provide insight into the issues associated
C Monitor system performance. with planning, designing, installing,
operating, and maintaining a surveillance
Surveillance is intended to provide support system.
for other elements in the system (e.g.,
incident detection, information C Provide a summary and description of
dissemination, ramp metering, etc.), not to available and emerging surveillance
drive the decisions about what system technologies.
elements should be included. In other

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MODULE SCOPE C Determining functions to be performed

by surveillance system.
The intent of this module is to help
engineers/planners in the decision process C Inventorying existing surveillance
involved in implementing an appropriate capabilities.
surveillance system. Included in this module
are a description of the decision process, a Table 3-1 describes the objectives for
summary of the components of a surveillance conducting each of the above tasks.
system, a discussion of available and
emerging surveillance technologies, and Identify and Locate Operational
examples of existing traffic management Problems
centers that are using various surveillance
technologies. In addition, special issues such This process involves identifying those
as privacy concerns and spacing freeways that would greatly benefit from the
requirements for sensors are addressed. use of surveillance and traffic management.
Areas benefiting the most would be those
3.2 DESIGN PROCESS with significant amounts of congestion.
There are two types of congestion:
This section describes the process for
planning, designing, and installing a C Recurring. Typically predictable and
surveillance system. Issues associated with occurs at locations where demand
operations and maintenance are also exceeds capacity or at geometric
addressed. The focus of this section is on bottlenecks (e.g., lane drops, high-
the decision process involved in volume entrance ramps, etc.).
implementing a surveillance system using a
systems engineering approach. Instead of C Nonrecurring. Caused by a random
focusing on technological solutions to event (e.g., incident, maintenance
perceived problems, the system engineering activity, special event, etc.) and has the
approach described in this section involves effect of reducing the capacity on a
identifying user needs and system specific section of freeway.
requirements first, and then designing a
system to meet these needs and Whether the congestion is recurring or non-
requirements. recurring, the effects on traffic operations
include:(1)
PROBLEM IDENTIFICATION
C Increased delay.
The first step in the decision process is to
identify the problems to be addressed by the C Slower and inconsistent travel speeds.
system. Issues that should be addressed in
the problem identification stage include the C Increased accident potential.
following:
C Other undesirable characteristics.
C Identifying and locating operational
deficiencies.

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Table 3-1. Tasks Involved in Problem Identification.

Task Objective
Identify Operational C Identify freeway sections to receive surveillance system
Problems
Determine Functions of C Evaluate freeway system to determine surveillance needs
Surveillance System C Determine type of data needed
C Determine importance of data
C Develop criteria for selecting detection technology
Inventory Existing C Determine if existing system needs to be replaced/expanded based
Surveillance on cost and needs
Capabilities C Estimate how long the existing system will be able to meet the
needs
C Identify advantages and disadvantages of existing system to aid in
the process of selecting new equipment

Other freeways that might be considered for C Detect incidents that have an impact on
surveillance include the following: traffic operations.

C Freeways in areas in which significant C Monitor incidence clearance.

increases in traffic demand are expected.
C Monitor traffic operations and support the
C Freeways in areas with significant implementation of control strategies (e.g.,
amounts of maintenance or construction lane control, ramp metering, etc.).
activities.
C Monitor environmental and pavement
C Freeways in areas with high frequencies of conditions (e.g., flood, ice, winds, fog,
traffic incidents. etc.).

These areas can expect an increase in Table 3-2 lists several scenarios in which
congestion, and surveillance in combination surveillance is used and typical methods that
with traffic management may be used as an meet the surveillance needs.
alternative to the very expensive solution of
building additional lanes. The type of surveillance system needed
depends not only on the purpose(s) that it
Determine Functions of Surveillance will serve, but also the type and importance
System of data to be collected. The following
sections discuss the types of data typically
A surveillance system can serve several collected through surveillance systems and
purposes, including the following: factors that should be considered when
determining the importance of the data.

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Table 3-2. Methods for Meeting Typical Surveillance Needs.

Need Method of Surveillance

Detect incidents and monitor incident removal Mainline detectors, vehicle probes, mobile
reports, closed-circuit TV
Meter ramps Mainline detectors, ramp detectors
Disseminate travel information to motorists Mainline detectors, vehicle probes, mobile
reports, closed-circuit TV
Monitor traffic during special event Closed-circuit TV
Inform motorists and/or maintenance personnel Environmental sensors, weather stations,
of icy conditions on freeways probe reports

Type of Data the field, and it is easy to explain and

understand. Speed measurements are
Traffic Measures. The measurements that typically taken for individual vehicles and
have traditionally been used to monitor averaged to characterize the traffic stream as
traffic operations on freeways include the a whole. Measured speeds can be compared
following: to optimum values to estimate the level of
operations for a freeway or to detect
C Volume. incidents. For example, an alarm for an
incident detection system might be set to go
C Speed. off if average speeds fall below a target
value. Taking speed measurements at
C Occupancy. different points along a freeway can help in
determining where congestion might exist.(1)
Volume is used to measure the quantity of
traffic and is defined as the number of Occupancy is defined as the percent of time
vehicles traveling a given section of freeway a given section of roadway is occupied and
over a period of time. The capacity of a can be used as a surrogate for density.
freeway represents the maximum volume of Occupancy is measured using presence
traffic that can pass a given roadway section detectors, and is much easier to obtain than
under prevailing roadway and traffic density. When occupancy is being
conditions. (2) As volume increases and measured, a single lane is usually considered,
approaches capacity, congestion will occur. with occupancy ranging from 0 percent (no
Volume is typically used to track historical vehicles passing over a section of roadway)
trends and to predict the future occurrence to 100 percent (vehicles stopped over a
of congestion on given freeway sections. section of roadway).

Speed is an important measurement in Although volume, speed, and occupancy

determining the quality of traffic operations. have been the traditional types of data
Speed is frequently used to describe traffic collected by a surveillance system, today’s
operations because it is easy to measure in traffic management centers also rely on other

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types of data for traffic management C To perform before/after analyses to

purposes. Examples of other data include determine the effects of implementing
the following: certain traffic management techniques.

C Vehicle travel times. C To create simulation models for analyzing

potential improvements.
C Bus location.
C To create planning models for establishing
C Emergency vehicle location. priorities for deployment.

C Queue length. Importance of Data

C Pavement condition. In the decision process involved in selecting

an appropriate surveillance system, the
Until recently, most of the data listed above importance of the data to be collected must
was difficult to measure in the field; be identified to establish the data
however, due to improvements in detector requirements. The following factors should
technologies, these measurements can now be considered when determining the data
be obtained. requirements:

Real-Time and Historical Data. Both real- C Speed.

time and historical data may be used for
traffic management purposes. Real-time C Accuracy.
data is needed for the following purposes in
a freeway management system: C Cost.

C Monitoring current traffic operating and The speed of a surveillance system relates to
environmental conditions. the frequency in which information about
field conditions is relayed to the traffic
C Detecting incidents. management center. Speed plays an
important role for some applications. For
C Implementing control strategies. example, in order to minimize the effects of
an incident on freeway operations, it is
Historical data refers to past traffic important to minimize the detection time. In
conditions on a given section of freeway. addition, the speed of data collection is
Historical data can be used for several important when the data is used to
purposes, including the following: implement a control strategy to reduce or
prevent the formation of congestion.
C To establish a record of past traffic
conditions on a certain freeway section. Other factors must be considered when
determining the speed of a surveillance
C To compare real-time data to historical system. The speed of the data collection
data to determine irregular traffic patterns; determines the amount of data to be
results of this comparison can be used to transmitted to the traffic control center.
detect traffic congestion and incidents. Therefore, operator overload should be
taken into consideration. In addition, the
amount and speed of data collection affects

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the type of communication system required. The capabilities of the existing

As the amount of data to be transmitted communications system should be evaluated,
increases, the communication requirements because the various detection technologies
increase. available have different communications
requirements. For example, transmitting
Data accuracy requirements are also full-motion video requires a wide
dependent upon the elements that the communication bandwidth (such as that
surveillance system is to support. For provided by fiber optic cable); however,
example, the accuracy of the data is transmitting only data requires considerably
important for incident detection systems to less bandwidth than can be met by most
avoid false alarms. Accuracy, however, may communication media.
not be as crucial when collecting traffic data
for traveler information systems. Typically, Existing infrastructure on which non-
the faster and more accurate a surveillance intrusive detectors and CCTV cameras may
system is, the more it is going to cost; be mounted should be identified at this stage.
therefore, it is important to balance speed, In addition, existing conduit for the
accuracy, and cost when choosing a communication system should also be noted.
system.(3)
IDENTIFICATION OF PARTNERS
Inventory Existing Surveillance
Capabilities Another important step in implementing a
successful surveillance system is to identify
The existing surveillance resources should be partners to be involved. Partners should be
identified and evaluated to determine if they considered in the following three areas:
are suitable for continued use. The
evaluation should include items such as the C Intra-agency (within agency).
following:(4) .
C Interagency (between agencies).
C Detectors.
C Additional resources.
C Controllers.
Intra-agency
C Communication media.
During the planning and design stages, all
It is important to determine if these interested groups and individuals that will be
components can meet existing needs and if involved in the surveillance system should be
they can accommodate changes in system identified and included in the decision
requirements. The existing surveillance making process. The project team should
system should be evaluated to determine if include representatives from the following
the required speed and accuracy of data areas:(4)
collection are attainable. Other factors that
should be considered are the reliability and C Management.
required maintenance of the existing system.
It may be more cost effective in the long run C Planning.
to replace a system that requires extensive
maintenance with a more reliable, low C Design.
maintenance system.

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C Operations. take place between the following public

transportation agencies:
C Maintenance.
C State.
Including representatives from each of these
areas will help ensure the success of the C City.
system. For example, it is important to
include persons from management on the C County.
team to help gain support for the
surveillance system. Since freeway C Transit.
management systems often compete for
funding with other agency expenditures, the C MPO.
support from top management is essential if
agency resources are to be allocated to the Sharing information about the occurrence of
operation and maintenance of the system. incidents between agencies permits joint
By including representatives from operations incident management by two or more
and maintenance, the following issues may agencies.(4) This allows more than one
be addressed: agency to be involved in responding to and
clearing incidents. Data exchange may take
C Support staff required for surveillance place between public transportation agencies
system. and the following enforcement and
emergency agencies and companies:
C Number and qualifications of existing
support staff. C Police.

C Training required to operate and maintain C Fire.

specific surveillance systems.
C Medical.
Using this team approach, specific concerns
and requirements from each area can be C Wrecker operators.
addressed from the beginning. The team
should then prioritize the requirements to Real-time traffic information may be relayed
determine which are most important and to the motorists through traveler information
which are desirable but not needed. systems such as dynamic message signs,
highway advisory radio, or in-vehicle
Interagency (Information Exchange) information systems. In addition, motorists
may be informed about traffic conditions by
During the operation of a traffic providing real-time traffic data to the
management system, it is important for following sources:
public agencies to exchange certain
information on a continual basis. C Media.
Information to be exchanged includes
scheduled maintenance activities and special C Cable television companies.
events. This coordination between agencies
will ensure that proper measures are taken to C Public kiosks.
minimize the effects of the event on overall
traffic operations. Data exchange should C Other traffic advisory services.

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Another private sector entity that benefits strengths and weaknesses. In addition,
from real-time traffic data is commercial researchers produce technological advances
vehicle operators. For example, dispatchers in surveillance systems.(4)
can use information about current traffic
conditions to re-route commercial vehicles in ESTABLISH GOALS AND
an effort to minimize delay for the OBJECTIVES
commercial drivers. This not only benefits
operators of the commercial vehicles, but it To establish the goals and objectives of a
also benefits other vehicles in areas of heavy system, it is important to identify what the
congestion by directing the commercial system is to accomplish. Goals are used to
vehicles away from the congested areas. define the long-range desires for the system.
Objectives define the level of performance
Additional Resources that is to be expected in the future. At this
stage, it is important to note that system
During the process of selecting the objectives are defined in terms of what
appropriate equipment to be used in the services and functions the system is to
surveillance system, it is important to provide — not in terms of technology. The
identify and evaluate all of the alternatives. focus should be on what the system is to
Because of the constant change in available achieve instead of on how it is to achieve it.
systems, the following groups should be
considered as resources during the planning As discussed earlier, the surveillance system
and design of a surveillance system:(4) provides support for other elements of a
traffic management system (such as incident
C Manufacturers. management, information dissemination,
. ramp control, etc.). Therefore, the goals and
C Suppliers. objectives of the surveillance system must
relate to the goals and objectives of the
C Users. elements that it is supporting. For example,
a goal of an incident management system is
C Researchers. to reduce the impact of incidents on traffic
operations. The objectives of the system
C Consultants. might be to detect an incident in less than
two minutes and reduce the incident
C Other interested groups or individuals. clearance time by five minutes. The
surveillance system can be evaluated by
Manufacturers continually develop and determining the system’s ability to meet
improve system capabilities and therefore these established objectives.
can provide information on the state-of-the-
art in surveillance technology. Information Since the goals and objectives of a
on the equipment specifications, functional surveillance system relate to those of the
and design features, and costs may be element that the surveillance system is
obtained from the manufacturers and supporting, the reader is referred to the
suppliers. Users of available systems specific modules within this report that
develop unique approaches for some systems address each element. Additional goals and
and can provide evaluations for certain objectives of a surveillance system might
technologies. Researchers and consultants include those that relate to monitoring the
test the available technologies to determine performance of a certain system. For

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example, a goal might be to ensure that the quantifiable measures. The measures
proper message is being displayed on a identified will be based on the elements of
dynamic message sign. Objectives would be the traffic management system that the
to determine if the sign was operational and surveillance component will support. In
to identify the message being displayed. addition, the established performance
Other goals and objectives of a surveillance measures will be based on local concerns and
system might relate to the effects of policies. Table 3-3 provides some examples
implementing certain control strategies. of performance measures that may be used
to evaluate a surveillance system.
ESTABLISH PERFORMANCE
CRITERIA DEFINE FUNCTIONAL
REQUIREMENTS
There is currently a wide range of traffic
detectors from which to choose, and with The next step in the decision process
advancements in technology, the number of involves defining all of the functions of a
alternatives is becoming even greater. It is system that are necessary to achieve the
important, therefore, to establish established objectives. At this stage, the
performance criteria to aid in the selection of focus should still be on what the system will
an optimum system. Establishing be designed to do, not how the system will
performance criteria allows alternative do it. Therefore, the functions should be
systems to be compared against these criteria defined independent of the available
in a later task. technology.

The established performance criteria should Again, the surveillance system provides
be related to the ability of the system to meet support to other elements in a traffic
the pre-established goals and objectives. management system. Therefore, the
Criteria that may be used to measure the functional requirements of a surveillance
performance of a surveillance system include system are dependent upon the element that
the following: it will support. For a surveillance system,
the functional requirements typically relate to
C Reliability of system. the type, frequency, and quantity of data
required. The data typically used for
C Accuracy of data. freeway surveillance have included measures
such as volume, speed, and occupancy;
C Timeliness of data. however, surveillance should not be limited
to these measures only. Additional measures
Each of the above criteria is important in might include travel time, queue length,
measuring the performance of a system. For headway, origin/destination, vehicle
example, a system is not effective if it classification, etc. These measures have
provides accurate data but produces it 30 been difficult to obtain in the past but can
minutes after it is needed. now be measured because of improvements
in technology.
The above criteria should be used to
establish parameters by which to evaluate the In the past, various surveillance concepts
system. The desired performance of the have been investigated in an attempt to meet
system together with a selected range of different functional requirements, and have
tolerance should be used to develop failed. Some of these concepts failed

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Table 3-3. Examples of Performance Measures for a Surveillance System.

Category Examples
Reliability C Percent of time that system produces desirable results in various
environmental conditions.
C Amount of maintenance required.
Accuracy C Percentage of false alarms generated from an automatic incident
detection system.
C Difference between a value measured by the detectors in the field
(e.g., speed, volume, etc.) and the actual value.
Timeliness C Average time between when an incident occurs and when it is
detected.
C Average time between when hazardous weather conditions occur
(e.g., ice, fog, flooding, etc.) and when they are detected.

because they were not appropriate; however, team should prioritize needs in order to
others have failed because of a lack of ability identify those that must be met and identify
to provide the needed data. Therefore, those needs that may be desirable but not
designers/planners should look at the various required. For example, a system to detect
alternatives for meeting the functional the location of incidents might be required,
requirements of a traffic management system but a system to monitor incident clearance
and not just at the traditional approach. might only be desirable.
Even though some concepts have failed in
the past, they may become viable alternatives DEFINE FUNCTIONAL
due to improvements in technology. RELATIONSHIPS, DATA
REQUIREMENTS, AND
Since the functional requirements of a INFORMATION FLOWS
surveillance system relate to those of
the element that the surveillance system is After functional requirements of a
supporting (e.g., ramp metering, incident in surveillance system are defined, the
the above section on establishing goals and relationships between functions, the data
objectives, additional requirements of a required by each function, and the
surveillance system might include those that information produced by each function must
are involved in monitoring the performance be defined. The National ITS Architecture
of a certain system. Table 3-4 shows Implementation Strategy defines the various
examples of functional requirements as they ITS elements in terms of market packages.(5)
relate to the goals and objectives of a This concept recognizes that various ITS
surveillance system. components must work together to achieve
system goals. They are “ tailored to fit-
In defining the functional requirements of a separately or in combination-real world
system, it is important to determine the transportation problems.”(5) The market
needs of all partners involved. The project packages related to surveillance are:

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Table 3-4. Examples of Functional Requirements Related to Monitoring

System Performance.

Goal Objective Functional Requirement

Ensure that proper message is Determine if sign is View operation of variable
being displayed on variable operational and identify message sign.
message sign. message being displayed.
Maximize benefits of a certain Determine the effects of the Monitor traffic operations
control strategy (i.e., ramp control strategy on traffic where control strategy has
metering, lane control, etc.). operations. been implemented.

C Network Surveillance Marketing IDENTIFY AND SCREEN

Package. This market package includes TECHNOLOGIES
the roadside sensors with appropriate
control and communication After the functional requirements and
infrastructure to interface with other architecture of the system have been defined,
market packages such as traffic the next step is to identify alternative
management and traveler information. technologies that can meet the defined
requirements. The following steps are
C Probe Surveillance Marketing involved in identifying and choosing the
Package. This market package is an appropriate technologies for the surveillance
alternative to traditional network system:
surveillance elements and does not
require the extensive distributed roadside C Identify alternative technologies.
infrastructure but does require wireless
communication between probe vehicles C Evaluate alternative technologies.
and other market packages such as
freeway control and surface street C Select the appropriate system.
control.
Identify Alternative Technologies
C Emissions and Environmental
Hazards Marketing Package. This There are a number of alternative
market package provides emissions and technologies available for collecting traffic
hazards information to the Traffic data. The characteristics, applications, and
Information Dissemination market requirements for various existing traffic
package. detection technologies are discussed in a
later section of this module. This review can
Development of the surveillance system be used as a starting point for identifying
should recognize the national architecture alternative technologies; however, due to
standards and be tailored to fit local issues continuous technological advancements and
and requirements. system improvements, available systems and
their capabilities are constantly changing.
Therefore, the current state-of-the-art in
surveillance technologies should be identified

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in this stage. To identify available each type of surveillance technology

technologies, it is important to continually included in the analysis:
interface with the following groups and
individuals during the identification C Location of sensors (i.e., embedded or
process:(4) non-intrusive).

C Manufacturers. C Installation, operation, and maintenance

requirements.
C Suppliers.
C Reliability.
C Users.
C Expected life.
C Consultants.
C Life-cycle costs.
C Researchers.
C Type of communications medium
C Other interested individuals. available.

By keeping in contact with these groups and C Requirements for future expansion.
individuals, the analyst can accomplish the
following: After the initial screening, the detailed
evaluation typically includes the following
C Keep up with current trends in steps:(4)
technology.
C Estimating costs and benefits of each
C Identify the advantages and alternative.
disadvantages of available systems.
C Performing comparative analyses.
C Obtain information on system
specifications and costs. C Selecting the system offering the greatest
potential.
Evaluate Alternative Technologies The advantages and disadvantages of the
system must be quantified or weighted and
The first step in evaluating alternative evaluated. There are many techniques
technologies is to identify the selection available to perform an analysis of the costs
criteria (see previous section, Establish and benefits for each alternative. Module
Performance Criteria). The next step 11 contains descriptions of procedures for
involves the following measures: performing a benefit-cost analysis.

C Initial screening of all available Select Appropriate Technology

technologies.
Surveillance technologies that are viable
C Detailed evaluation of the remaining alternatives should have benefits that
alternatives. outweigh the costs. The argument can be
made that the best system will have the
During the initial screening process, the greatest benefit-cost ratio; however, this is
following factors should be considered for

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not always the case. For example, a simple, Specifications

low-cost system with fewer benefits may
have the same benefit-cost ratio as a more Specifications contain detailed information
sophisticated, affordable system with more on the minimum acceptable standards for the
benefits. Therefore, the analysis should surveillance system’s equipment along with
include allowable expenditures for the procedures on how the equipment should be
system and the net benefits of each installed. Detailed specifications are
alternative.(4) important to ensure that the proper
equipment is obtained. Sources for
PLAN DEVELOPMENT equipment and materials specifications
include the following:(4)
After the technologies that will be used in
the system have been selected, the next step C Federal Highway Administration.
is to develop a plan for implementation. The
Implementation Plan documents the results C Institute of Transportation Engineers.
of the previous steps and identifies how the
system will be implemented in the field. The C Other State transportation departments.
Implementation Plan should also assess the
phasing, procurement, staffing, and funding These specifications may be used as they
options available for implementing the exist or modified to fit particular needs.
system. Module 2 contains a description of Guidelines for specifications for the various
elements that should be included in the components of a surveillance system are
Implementation Plan. provided in table 3-6.(4)

One of the tasks at this stage is to develop IDENTIFY FUNDING SOURCES

the design plans and specifications. This
task involves transforming the needs and As described in Module 2, funding sources
goals of the surveillance system into design should be identified during the development
documents and specifications suitable for of the Implementation Plan. Funding for
competitive bids. The plans include surveillance systems may come from both
drawings that show the physical layout of the Federal and State levels. On the Federal
the system, and the specifications define the level, funding is available through the
quality and type of workmanship and Intermodal Surface Transportation
materials. (4) Efficiency Act (ISTEA) and continuing with
the proposed National Economic Crossroads
Design Plans Transportation Efficiency Act (NEXTEA).
Under the ISTEA act, capital and operating
The design plans provide information for the expenses for traffic management programs
contractor and equipment supplier to are eligible for Federal aid. By including
prepare a project bid and for the projects in the Transportation Improvement
construction manager to aid in controlling Program (a spending plan required by the
the construction. Table 3-5 shows typical Federal government), agencies can receive
information that should be provided on the federal funds. Under Title 23 of the United
design plans. (4) States Code (as amended by the ISTEA of
1991) the following funding sources can be
used to purchase and operate freeway
management surveillance systems:

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Table 3-5. Typical Information in Design Plan. (4)

Item Description
Title Sheet Shows name, location, and scope of project.
Summary of Shows material and equipment quantities.
Quantities
General Notes Frequently call special attention to critical requirements to ensure they
are not overlooked; must avoid conflicts with specifications.
Site Schematics Scale drawings of each site showing the roadway geometry, location
of poles, conduit locations, and any other pertinent site information.
Construction Design Shows locations of detectors to be installed and minimum
Drawings requirements for construction dimensions.
Traffic Control Plan Indicates handling of traffic during construction.
Details of Barricades Illustrates the construction phase of the project.
and Signing
Diagram of Shows details of location.
Underground Utilities
Standard Plans Possessed by each agency, generally provide numerous standard
drawings of frequently encountered details already approved for use
in situations applicable to the project.

Table 3-6. Guidelines for Specifications. (4)

Specification Guidelines
Detectors Include physical properties, electrical
properties, environmental conditions under
which the equipment must operate, controls,
and methods of operation.
Computer Software Provide functional specifications for control
software, compilers, assemblers, utilities, and
diagnostic programs.
Video Terminals Specify sample operator screens and controls,
screen size, refresh rate, and colors.
CCTV Monitoring Specify monitors, cameras, and interface
protocols.

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C Surface Transportation Program (STP). process. Additional issues that should be

considered when implementing a surveillance
C National Highway System (NHS). system include the following:

C Congestion Mitigation and Air Quality C Phasing of installation.

Program (CMAQ).
C Training.
STP funds are available on eligible projects
with no time limit. NHS and CMAQ funds During the installation of a surveillance
have definite time limits, and cannot be used system, some disruptions to traffic are to be
for maintenance.(6) expected. To minimize delay to traffic,
construction should take place during off-
Although some Federal funds are available peak hours. In addition, the maximum
for operating costs, Title 23 funds are number of lanes that can be simultaneously
generally used for system deployment and closed should be specified.(4) When possible,
start-up assistance. Typically, funding for phasing of installation for the surveillance
both operations and maintenance costs are system should be coordinated with other
provided on the State and local levels freeway construction to minimize the overall
through maintenance budgets. Funding delay to traffic.
operations and maintenance costs for
surveillance systems through the Another area that must be addressed during
maintenance budgets often causes problems the implementation of a system is the
because of competition from other development of training programs for
traditional maintenance activities. operators and maintenance personnel.
Therefore, it is crucial to identify the funding Training should provide the technical skill
needs and funding sources for operation and necessary to effectively operate and maintain
maintenance activities early in the decision the system. The amount of training required
process. depends upon the qualifications and
knowledge of existing personnel and the
Public/private partnership is an approach requirements of the new system. For
that many agencies are using to increase the example, maintenance personnel that are
source of funding for traffic management familiar with an inductive loop detection
purposes. For example, many cellular system will require extensive training to
telephone companies offer free or reduced maintain a video image processing system.
rates to agencies for incident detection Additional information concerning training
purposes. This approach allows other requirements is contained in reference 9.
partners to get involved in a fair and
equitable manner. EVALUATION

IMPLEMENTATION After a surveillance system has been

installed, the system should be evaluated for
The implementation process includes the its effectiveness in meeting the objectives.
activities involved in installing the The objectives of a surveillance system may
components of the surveillance system to include any of the following:
meet the established goal and objectives.
Module 2 gives a description of issues to be C Monitoring traffic operations.
addressed during the implementation

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C Detecting incidents. speed, occupancy, etc.) measured upstream

and downstream from an incident.
C Supporting implementation of control
strategies. After an incident detection system has been
implemented, it must be monitored and
C Monitoring environmental conditions. evaluated to calibrate the incident detection
algorithm. The system is monitored by
Monitoring Traffic Operations detecting incidents through alternative means
such as the following:
The goals of monitoring traffic operations
include: C CCTV.

C Providing measures of traffic operations C Mobile reports (cellular call-ins, call

(e.g., speed, flow, density, etc.). boxes, service patrols, etc.).

C Identifying locations of congestion. C Emergency channels.

C Indicating the severity of congestion. The algorithm is calibrated by adjusting the

threshold values. The measure of
Records should be kept to track system effectiveness typically used for calibration is
operations and note any problems. An the false alarm rate. Threshold values are
overall evaluation of the equipment should adjusted until an acceptable false alarm rate
include monitoring the following: is achieved. The acceptance level is
dependent upon available means of verifying
C System reliability. the incident. For example, if an incident can
be verified using CCTV, then a higher
C Ability to provide required data. acceptance level might be tolerated. The
threshold values may need to be recalibrated
C Timeliness of data. for major operational or geometric
changes.(7)
C Accuracy of data.
Implementing Control Strategies
C Ability to perform under various
environmental conditions. There are two types of control systems that
may be used for freeways:
C Operational and maintenance
requirements and costs. C Lane use control (see Module 4)
.
C Any other problems with system. C Ramp control (see Module 5).

Detecting Incidents The objectives of these systems are to meter

the demand or prohibit a certain movement
Automatic incident detection systems apply in order to keep freeway volume below
data collected from the field equipment to capacity to ensure continuous movement on
computer algorithms. The algorithms are the freeway. Detectors provide traffic data
designed to detect incidents by identifying to these control systems to aid in the
discontinuities in traffic operations (e.g.,

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decision making process about the extent to Additional conditions that require
which control should be implemented. The monitoring in tunnel sections include
detectors used in a control system should be noxious gases, such as carbon monoxide.
evaluated based on the following criteria:
The evaluation of environmental detection
C Reliability of detectors. systems should include the following
determinations:
C Ability to provide needed data.
C Ability to meet established goals.
C Timeliness of data.
C System reliability.
C Accuracy of data.
C Ability to provide required data.
Monitoring Environmental Conditions
C Timeliness of data.
Typical environmental conditions on
freeways that are monitored include the C Accuracy of data.
following:
C Operational and maintenance
C Ice. requirements and costs.

C Wind. C Any other problems associated with

system.
C Fog.

C Rain. 3.3 TECHNIQUES AND

TECHNOLOGIES
C Dust.
SYSTEM COMPONENTS
The goals of monitoring these conditions
include the following: The complexity and size of a surveillance
system will vary with the size of the freeway
C Warn drivers of dangerous driving system being monitored and with the specific
conditions. functions that it will perform. For example,
when the area being surveyed is relatively
C Reduce number of incidents. small, a section of the traffic engineering
offices may be sufficient to house the control
C Reduce secondary incidents. center. As the system expands and the
responsibilities of the control center increase,
C Help maintenance personnel monitor a larger center with more sophisticated
pavement conditions. equipment may be required. Figure 3-2
shows a simple example of the control
C Improve response time. center components included in a surveillance
system.
C Reduce costs associated with monitoring
and treating ice on pavements.

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Manual TABLE OF CONTENTS Module 3. TABLE OF CONTENTS

Communications
Shadowed
Disks
Computer 1 Computer 2

Local Area Network

Monitor CCTV Print Graphical Video

Controls Server Display Tape
Recorder
Programmer’s Printer
Console

Operator Workstation

Figure 3-2. Control Center Components Typically Included in a Surveillance

System.

The components of a surveillance system surveillance purposes. These technologies

include the following: can be divided into the following groups:

C Detection methods. C Embedded detectors.

C Hardware. C Non-intrusive detectors.

C Software. C Vehicle probes.

C Communications. C Mobile reports.

Table 3-7 provides a list of typical system C Closed-circuit television cameras.

components.
C Environmental sensors.
Detection Methods
Available detection methods are listed in
There are many technologies available for table 3-7. Descriptions of each of these
collecting traffic and environmental data for technologies is provided in a later section,
entitled Surveillance Technologies.

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Manual TABLE OF CONTENTS Module 3. TABLE OF CONTENTS

Table 3-7. Typical Components for a Surveillance System.

Component Alternatives
Detection Methods Inductive Loop
Magnetometer
Microwave Radar
Infrared
Ultrasonic
Acoustic
Video Image Processing
Automatic Vehicle Identification
Automatic Vehicle Location
Cellular Telephone Probes
Cellular Call-Ins
Freeway Service Patrol Reports
Call Boxes/Emergency Telephones
Closed-Circuit Television
Environmental Detectors
Hardware Computers
Disk Drives
Printers
Monitors
Controllers
Displays
Video Tape Recorders
Software Incident Detection Algorithm
Real-Time Expert System
Interface Software
Communications Internal
- Local Area Network
External
- Fiber Optic
- Coaxial
- Twisted Pair
- Microwave
- Radio
- Cellular Telephone
- Citizen Band Radio

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Manual TABLE OF CONTENTS Module 3. TABLE OF CONTENTS

Hardware for operating the CCTV system are also

located at the workstation. The operator
Computers play significant roles in the may have software installed on the personal
operations of a surveillance system. The computer to control the cameras or may
functions performed by the computers in the have a separate control panel. Camera
control center include the following:(7) controls usually include camera selection,
pan, tilt, zoom, and focus.
C Reception of data transmission from the
field devices. The printers interface with the local area
network communication system through the
C Transmission of data from the control use of print servers. Printers may be used
room to the field equipment. to provide any of the following:(4)

C Reception of operator commands from C Hard copy reports of mode status and
keyboards or control panels. equipment failure logs.

C Control of graphical displays. C Traffic data summaries.

C Data processing to perform such C Database status summaries.

functions as detecting incidents, deriving
traffic flow characteristics, and C Special reports requested by the
identifying equipment failures. operator.

C Storing data to create a historical C Logs of system operations.

database.
The functions of graphical displays are to
Computer 1 in figure 3-2 is an online provide observations of system operations
computer that receives and transmits and camera field of views for CCTV.
information to and from the field devices. Graphics may be provided on monitors at the
Computer 2 serves as a backup and performs workstations or on a large screen graphics
offline functions such as program display. The large screen displays have
development and database updating. The generally replaced the wall map displays
computers are typically microprocessor used in older centers. The display may
versions of minicomputers. The disk consist of a projection video display, a large
shadowing feature transfers data from the video screen, or an array of smaller video
online computer to backup a system.(4) screens. This new system has proven to be
much easier to modify when new systems
The operator workstation typically consists come online than the wall map system.(4)
of a personal computer unit. Functions that
take place at the workstation include Another important component of a
monitoring traffic operations, incident surveillance system is the video tape
detection, decision making, and recorder. Traffic operations can be recorded
implementation of control strategies. for analyzing and comparing conditions over
a given period of time or for demonstration
Closed-circuit television (CCTV) can be purposes. Depending on the size of the
used for monitoring traffic conditions or system and the recording requirements, one
detecting and confirming incidents. Controls or more recorders can be provided to

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Manual TABLE OF CONTENTS Module 3. TABLE OF CONTENTS

interface with any camera in the system.(7) Real-Time Expert Systems

Some traffic management centers choose not
to record and archive incidents because of Real-time expert systems are currently being
the potential drain on their staff (video tapes developed for application in traffic operation
requested by claims adjusters, lawyers, centers. These expert systems provide
private citizens, etc.) and the possiblity of decision support for operations personnel so
having to appear in court. they can more efficiently carry out their
functions.(8) The knowledge-based support
Software is based on the knowledge of experts in the
field of traffic management. Functions of an
Software is an important component of a expert system include:(8, 9)
surveillance system. Without software, the
data collected by the surveillance system has C Detecting, verifying, and estimating the
little value. severity of incidents.

Three general types of software used with C Providing advice in areas such as
surveillance systems include the following: dispatch of traffic and incident
management teams.
C Software such as incident detection
algorithms, etc. that apply the data C Developing and coordinating messages
supplied by the surveillance system on variable message signs and other
methods of information dissemination.
C Software that supports the operations
support software such as real-time C Controlling traffic with lane control and
knowledge-based systems. ramp control systems.

C Software for interfacing and The University of California at Irvine is in

communicating with the field devices. the process of developing a prototype real-
time knowledge-based expert system called
Incident Detection Algorithms FRED (Freeway Real-Time Expert System
Demonstration). The expert system uses
One of the primary objectives of a advanced processing capabilities to integrate
surveillance system is to detect non- diverse types of traffic surveillance data for
recurring congestion, such as that caused by freeway monitoring and control purposes.
an incident. Incidents cause significant After detecting an incident, the system uses
amounts of delay for freeway vehicles; additional information from several sources
however, because they are random, they are to formulate appropriate responses. The
impossible to predict and difficult to detect. information includes the following:(10)
Incident detection algorithms attempt to
automatically detect incidents based on field C Traffic data from detectors (e.g., speed,
data received from detection equipment. volume, occupancy, etc.).
Module 7 provides further discussion on
incident detection algorithms. C Information on traffic conditions from
CCTV.

C Field reports from police officers and

other official personnel.

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Manual TABLE OF CONTENTS Module 3. TABLE OF CONTENTS

C Cellular and emergency telephone calls The knowledge-based support in FRED

from motorists. comes from the real-time expert system
shell, G2. This system has the ability to
Figure 3-3 illustrates the overall system determine what data is required at any
layout of FRED.(10) In terms of incident particular stage, and to send for it. Given
detection and verification, this system is the incoming data, decisions are made on the
consistent with many traffic operation basis of a predetermined set of rules. Once
centers around the country. The system uses an incident has been detected and verified,
two methods to detect incidents: the system recommends actions to be taken,
such as using ramp metering or closing a
C An incident detection algorithm on a ramp.(10)
central computer receives 30-second
occupancy counts from freeway loop Communications
detectors and notifies FRED if an
incident is detected. Communications between the major
components in the control center are
C Outside reports from various agencies accomplished through a local area network
and motorists are received by a (LAN). The benefits of a LAN architecture
communications center that filters the include the following:(4)
reports and sends the high priority ones
to FRED.

(10)
Figure 3-3. External System Overview for Real-Time Expert System.

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Manual TABLE OF CONTENTS Module 3. TABLE OF CONTENTS

C Facilitate the addition of components to The discussion is organized under the

the network. following headings:

C Serve more devices in the operations C Embedded Detectors.

center.
C Non-intrusive Detectors.
C Interface with additional field devices
and controllers. C Vehicle Probes.

C Communicate with additional outside C Mobile Reports.

agencies and traffic data users.
C Closed-circuit Television Cameras.
Communications between the control center
and the field devices occur through an C Environmental Sensors.
external communication system. There are
two basic categories of communication Table 3-9 provides a summary of the
media: detectors discussed in this section. The
majority of detectors used for traffic data
C Physical cable (fiber optic, coaxial, collection purposes are of either the
twisted pair). embedded or non-intrusive type. Within
these two groups, there are many alternative
C Airwave transmissions (microwave, detectors, and each has advantages and
radio, and cellular telephone). disadvantages.

The type of communication medium required Table 3-10 provides summaries of the
depends on the type of detection equipment characteristics for embedded and non-
being used. For example, transmission of intrusive detectors that are either currently
video data requires a wide bandwidth that available or in the developmental stage.
exceeds the capacity of many communication The following discussions will address each
media. Transmission of voice and traffic of these detectors in more detail. The
data, however, requires a much narrower following areas are addressed for each traffic
bandwidth which can be met by standard detector discussed:
communication media. Table 3-8 lists some
available communication media and their C Characteristics.
capabilities.(3) Module 9 provides a detailed
discussion of communication systems. C Applications.

SURVEILLANCE TECHNOLOGIES C Installation requirements.

There are many technologies available for EMBEDDED DETECTORS

collecting traffic data. Although inductive
loop detectors are currently used more than An embedded detector system consists of
any other method, other technologies are sensors in or below the surface of the
beginning to replace loop detectors in many roadway. These detectors are currently the
applications. This section provides most widely used form of vehicle detection.
descriptions of currently available detectors. The main detectors being used include the
following:

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Manual TABLE OF CONTENTS Module 3. TABLE OF CONTENTS

Table 3-8. Communication Media. (3)

Distance
Medium Type Data Type Bandwidth Capabilities
Fiber Optic Physical Video, digital, voice High Long
Coaxial Physical Video, digital, voice Moderate Short
Twisted Pair Physical Digital, voice Low Long
Microwave Airwave Video, digital, voice High Line-of-Sight
Radio Airwave Digital, voice Low Long
Spread Spectrum Airwave Digital, voice Low Line-of-Sight
Cellular Telephone Airwave Digital, voice Low Moderate
Citizen Band Radio Airwave Digital, voice Low Moderate

C Inductive loop detector. The loop system becomes active when the
detector unit sends an electrical current
C Magnetometers. through the cable, creating a magnetic field
in the loop. When a vehicle passes over the
Inductive Loop Detector loop, the ferrous material in the vehicle
causes a decrease in the inductance of the
Characteristics circuit. This increases the frequency of
oscillation that is sensed by the detector unit.
The inductive loop detector (ILD) is by far
the most common form of detector used for Applications
traffic management purposes. Figure 3-4
illustrates the used of loop detectors for Loop detectors can measure many traffic
freeway surveillance purposes. The principal parameters including the following:
components of an inductive loop detector
include the following:(11) C Vehicle count.

C One or more turns of insulated wire C Speed.

buried in a narrow, shallow saw-cut in
the roadway. C Occupancy.

C Lead-in cable that connects the loop to C Presence.

the detector via a roadside pull-out box.
C Vehicle classification.
C Detector unit (or detector amplifier) that
interprets changes in the electrical Loop detectors can operate in either a pulse
properties of the loop when a vehicle or presence mode. In the pulse mode, a
passes over it. short signal (typically 0.125 s) is sent from

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Manual TABLE OF CONTENTS Module 3. TABLE OF CONTENTS

Table 3-9. Summary of Detectors.

Detector Type Detector Data Collection Information Type

Embedded Inductive Loop Site Specific Data
Magnetometer Site Specific Data
Non-Intrusive Radar Site Specific Data
Infrared Site Specific Data
Ultrasonic Site Specific Data
Acoustic Site Specific Data
Video Imaging Site Specific Video, Data
Vehicle Probes Automatic Site Specific Data
Vehicle
Identification
Automatic Variable Location Data
Vehicle Location
Cellular Variable Location Data
Telephone Probes
Mobile Reports Cellular Reporting Variable Location Voice
Service Patrols Variable Location Voice
Call Boxes Site Specific Coded Message
Closed-Circuit Fixed Location Variable Location Video
Television Cameras
(CCTV)
Portable Cameras Variable Location Video

Environmental Freeways Site Specific Data

Sensors
Tunnels Site Specific Data

the loop to the detector unit and can be used measurements. Presence detection is used
to provide volume counts. In the presence for most detector applications, and is the
mode, the signal that is sent to the detector preferred mode for most system
unit lasts as long as the vehicle is in the management purposes.
detection area. Presence detectors are used
to provide volume counts and occupancy

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 Manual TABLE OF CONTENTS
Table 3-10. Summary of Traffic Detectors.

Detector Type Detector Description Advantages Disadvantages

Embedded Inductive Loop Coil of cable embedded in the C Flexible design. C Installation requires pavement
pavement surface that creates a C Wide range of applications. cuts.
magnetic field. Vehicle is detected C Provides basic traffic parameters C Installation and maintenance
when this magnetic field is (e.g., volume, speed, presence, requires lane closure.
disturbed. occupancy). C Detectors subject to stresses
of traffic.

Magnetometer Small cylinders containing sensor C Can be used in situations where C Installation requires pavement
coils that operate in a manner loops are not feasible (e.g., bridge cuts.
similar to inductive loops. decks). C Installation and maintenance
Developed as alternative to loop C Less susceptible than loops to require lane closure.
detectors for special situations. stresses of traffic. C Small detection zone.
C Typically used onlyto provide
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count and occupancy.

Non-Intrusive Microwave Radar Transmits electromagnetic energy C Generally insensitive to weather C Requires FCC license for
toward vehicles on roadway. conditions. operation and maintenance.
Traffic parameters are calculated by C Provides day and night operation. C May lock on to the strongest
measuring the return signal signal (e.g., large truck).

Module 3. TABLE OF CONTENTS

frequency from vehicles.

Infrared Active infrared detectors transmit C Active detector emits narrow C Operation affected by
electromagnetic energy. Passive beam allowing for accurate precipitation (e.g., rain, fog,
infrared detectors do not transmit determination of vehicle position. etc.).
energy but measure the amount of C Provides day and night operation. C Difficulty in maintaining
energy that is emitted by objects in C Provides most basic traffic alignment on vibrating
the field of view. parameters. structures.
C Passive detectors can be used for
strategic loop replacement.
 Manual TABLE OF CONTENTS
Table 3-10. Summary of Traffic Detectors (cont.).

Detector Type Detector Description Advantages Disadvantages

Non-Intrusive Ultrasonic Transmits sound waves at C Provides most basic traffic C Environmental conditions (e.g.,
(Continued) frequencies between 20 and 200 parameters. temperature, humidity, air
kHz. Detects vehicle by measuring turbulence, etc.) can affect
return waves. performance.
C Snow covered vehicles are difficult
to detect.
C High level of special maintenance
capability is required.

Acoustic Uses microphones along with signal C Completely passive. C Relatively new technology for
processing technology to listen for C Generally insensitive to weather traffic surveillance.
3-31

sounds associated with vehicles. conditions.

C Provides day and night operation.

Video Image Video image processors receive C Location or addition of detector C Inclement weather, shadows, and
Processing information from video cameras and zones can easily be done. poor lighting can affect
use algorithms to analyze the video C Provides basic traffic parameters. performance.

Module 3. TABLE OF CONTENTS

image input. C Provides wide-area detection. C May require significant processing
power and a wide communication
bandwidth.
Manual TABLE OF CONTENTS Module 3. TABLE OF CONTENTS

Figure 3-4. Inductive Loop Detectors Used for Freeway Surveillance. (12)

Loops can be used to detect vehicle speeds maintenance of ILDs is contained in the
by placing two loops in pulse mode a short Traffic Detector Handbook.(11)
distance apart (see figure 3-5).(4) The
distance between the loops divided by the The most important process in implementing
time required for a vehicle to travel between a loop detection system is the one related to
the loops provides the speed of the vehicle. the installation procedures. Installation
procedures will have a significant effect on
Installation Requirements the long term operational effectiveness of the
detector system. Improper installation
The ILD provides for a wide range of techniques may result in detector failures and
vehicle detection because of the flexibility of require extensive maintenance. Installing the
its design. Loop configurations are generally wire loops in the pavement requires the
grouped into two areas: short loops and long following steps:
loops. For vehicle detection, the short loop
configuration is recommended. The most C Cutting a slot in the pavement.
common loop size for traffic management
purposes is 1.8 m by 1.8 m (6 ft by 6 ft). C Cleaning and drying the slot.
The maximum length of a short loop should
be 3.1 m (10 ft).(3) Detailed information C Laying in the detector wire.
concerning the design, installation, and
C Sealing the saw cut.

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Manual TABLE OF CONTENTS Module 3. TABLE OF CONTENTS

Figure 3-5. Typical Loop Installation for Measuring Speed. (4)

C Connecting the wire loop to the lead-in C Deterioration of wire insulation.

cable.
C Poor sealants or inadequate sealant
C Connecting the lead-in cable to the application.
detector unit.
C Inadequate splices or electrical
The main concern with the use of ILDs is connections.
reliability. Because the detectors are
embedded within the pavement, they are C Damage caused by construction
subject to the stress of traffic traveling on activities.
them and to pavement deterioration. In
northern States, other problems are C Improper detector unit tuning.
associated with freeze-thaw conditions.(13)
C Detector unit failure.
The primary causes of loop failure include
the following: C Lightning/electrical surges.

C Pavement problems (cracking and Most of these problems can be traced back
moving). to improper installation techniques.

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Manual TABLE OF CONTENTS Module 3. TABLE OF CONTENTS

Magnetometer Installation Requirements

Characteristics Similar to the installation of inductive loops,

installing magnetometers requires cutting the
Magnetometers contain small probes that pavement; however, because magnetometers
range in size from 5 cm (2 in) to 11 cm (4.25 are more compact in size, not as much
in) in diameter. The magnetometer was cutting is required. Detailed information
developed as an alternative for loop concerning the design, installation, and
detectors in special situations, such as bridge maintenance of magnetometers is contained
structures. Figure 3-6 illustrates a typical in the Traffic Detector Handbook.(11)
installation for magnetometers. Similar to
loop detectors, the components of a For a magnetometer to detect a vehicle,
magnetometer detection system include the some part of the vehicle must pass over the
following:(11) probe. Therefore, optimum lateral placement
of probes in the pavement is dependent upon
C One or more small probes (sensors) the following factors:
embedded in the pavement.
C Width of narrowest vehicle to be
C Probe cable. detected.

C Lead-in cable that connects the probe to C Width of lane.

the detector via a roadside pull-out box.
C Required detection quality.
C Detector unit.
Since most vehicles are wider than 1.5 m (5
Magnetometers measure the density of ft), a single probe might not be adequate for
vertical flux lines of the earth’s magnetic lane widths greater than 3 m (10 ft). For
field. When a vehicle passes over the probe, lane widths of 3.7 m (12 ft), two probes per
the ferrous material in the vehicle increases lane should be adequate for detecting all
the density of the flux lines. Magnetometers four-wheeled vehicles.
sense this increase and interpret it as the
presence of a vehicle. Installing the magnetometers requires
placing the detectors in the pavement. The
Applications installation procedures include the following
steps:
Magnetometers can operate in either
presence of pulse modes and are most C Drill holes in pavement for probes.
effective in determining occupancy and
volume. This type of system is usually used C Saw slots in pavement for detector
when the only information required is that a wires.
vehicle has arrived at a specific point.(11)
Speed can also be measured by placing two C Clean and dry saw cuts.
sets of probes a known distance apart.

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Manual TABLE OF CONTENTS Module 3. TABLE OF CONTENTS

Figure 3-6. Typical Layout for Magnetometer Installation.(4)

C Place each probe in the proper hole. the maximum distance from steel supports
(see figure 3-7). The presence of steel over
C Secure probe with housing, sand, or or under the probes has little effect on
sealant. performance; however, vertical structural
steel members may influence the magnetic
C Connect detector wire to lead-in cable. field surrounding the probe, and affect
performance.
C Connect lead-in cable to the detector
unit. The causes of magnetometer failures are
usually either improper installation or
C Test system. maintenance procedures. The major factors
that affect the operation of a magnetometer
C Seal drilled holes. detector system include the following:

Because the probes are buried several C Proper burial depth of probe.
centimeters below the surface of the
pavement, magnetometers are less C Stability of the probe in the pavement.
susceptible than ILDs to deteriorating
pavement conditions. Therefore, C Moisture penetration into the probe
magnetometers are primarily used in cable.
northern States that suffer pavement
deterioration due to freeze-thaw cycles. In C Saw slot maintenance.
addition, the magnetometer can usually be
used on bridge decks where cutting the NON-INTRUSIVE DETECTORS
pavement for loop installation is not an
option. In response to an increasing demand for
alternatives to loop detectors, a broad range
When using magnetometers on bridge of non-intrusive detectors have become
structures, the probes should be placed at

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Manual TABLE OF CONTENTS Module 3. TABLE OF CONTENTS

Figure 3-7. Typical Bridge Deck Installation for Magnetometer. (4)

available. (14) Non-intrusive detectors are

mounted on a structure above the surface of
the pavement. Figure 3-8 shows an example
of a non-intrusive detector. Advantages that
non-intrusive detectors have over embedded
detectors include the following:(15,16)

C Modifications to pavement are not

required for installation.

C Detectors can be moved or replaced

more easily.

C Lane closure may not be required during

installation and maintenance.

C Detectors are not subject to stresses of

traffic.

C Detectors can be used during and after Figure 3-8. Example of Non-Intrusive
any reconstruction or maintenance Detector. (17)
activities.

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Manual TABLE OF CONTENTS Module 3. TABLE OF CONTENTS

A disadvantage of non-intrusive detectors is C Continuous wave.

that they may produce unreliable results
during adverse weather conditions. C Frequency modulated continuous wave
(FMCW).
Over the past few years, however,
improvements in technology have improved C Pulsing waveform.
the performance and reliability of certain
non-intrusive detectors, and costs have Continuous Wave. With constant wave
become more and more competitive with radars, electromagnetic energy is transmitted
loops. There are currently many non- at a constant frequency. This type of radar
intrusive technologies that provide viable is the most common form of radar detection.
alternatives to loop detectors. These As shown in figure 3-9(a), vehicle speeds are
alternatives include the following: calculated by measuring the Doppler shift
that occurs in the return signal frequency.
C Microwave radar. The shift in the return signal is proportional
to the speed of the vehicle. Because only
C Infrared. moving vehicles cause a frequency shift in
the return signal, these detectors cannot
C Ultrasonic. detect stationary vehicles, and thus cannot be
used as presence detectors.
C Acoustic.
Frequency Modulated Continuous Wave
C Video image processing. (FMCW). FMCW radar detectors can be
used to measure the presence of vehicles as
Microwave Radar well as the speed. Figure 3-9(b) illustrates a
typical waveform of these types of detectors.
Characteristics Presence detection occurs in the portion of
the waveform where the frequency changes
Microwave radar detectors have been used with time. The portion of the waveform that
in both law enforcement and traffic is constant is used to measure the speed of
management for some time to monitor vehicles in the same manner as the
vehicle speed. For traffic management, radar continuous wave detectors.
sensors are mounted either above or beside
the road and direct a beam of microwave Pulsing Waveform. Pulsing waveform is a
energy onto a detection area. Most radar variation of the FMCW signal. As illustrated
detectors transmit electromagnetic energy at in figure 3-9(c), it is generated by using
the speed of light at the K-band (24 gHz) or differences in frequency change rates, time
the X-band (10 gHz).(18) duration of each waveform segment, and
numbers and sequencing of the waveforms.
The form of the electromagnetic wave Detectors that use this type of waveform can
transmitted by the detector determines the measure differences between the range to the
type of data that can be obtained by the unit. road and the vehicle, making it possible to
Three types of radar frequency include the provide not only vehicle counts and presence
following:(18) detection, but also occupancy. Speeds can
also be determined by measuring the elapsed
travel time between two detectors.

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Manual TABLE OF CONTENTS Module 3. TABLE OF CONTENTS

Transmited Signal
Doppler Frequency Shift
From A Moving Vehicle
Received Signal

Time
a. Continouus wave energy

Time
b. FMWCW waveform

Pulse Width

Pulse Repetition Interval

Time

c. Pulse waveform

Figure 3-9. Waveforms Used with Microwave Detectors. (18)

Depending on the width of the radar beam, Narrow Beam. Narrow beam detectors
radar detectors may be used to monitor from monitor only a single lane of traffic in one
one to several lanes. Three types of radar direction (see figure 3-10(b)). They are
detectors exist:(13) typically installed where freeway lanes have
varied uses (e.g., through lanes and exit
C Wide beam. lanes, or through lanes and HOV lanes).

C Narrow beam. Long-Range. Long-range detectors project

the radar beam over greater distances, up to
C Long-range. 245 m (800 ft). This type of detector may
be installed alongside a freeway with traffic
Wide Beam. Wide beam detectors monitor traveling in one direction to measure speeds
all lanes of traffic in one direction of the of freeway traffic traveling in the opposite
freeway (see figure 3-10(a)). They provide direction (see figure 3-10(c)).
information on the overall traffic speeds;
however, every vehicle is not detected. One advantage of radar detectors is that they
can discriminate between approaching and
receding traffic. (15) This capability would be

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Manual TABLE OF CONTENTS Module 3. TABLE OF CONTENTS

some radar units can measure vehicle

profiles to perform classification counts.(18)

An area in which the use of microwave radar

detectors is increasing is incident detection.
Incident detection algorithms used with
radar detectors typically detect incidents by
using speed data. This differs from the
majority of incident detection algorithms,
which detect incidents based on occupancy
data. A recent study suggests microwave
radar incident detection systems are highly
accurate and reliable.(13)

One of the biggest advantages of microwave

radar detectors is their ability to perform
adequately in all weather conditions.
Because the detectors are mounted above
the pavement surface, they are not subject to
the effects of ice, sand, and salt during the
winter months, as are many embedded
detectors. Microwave radar detectors can
be useful under the following
(13,19,20)
conditions:

C Rain.

C Fog.

C Snow.

Figure 3-10. Alternative Radar Beam C High winds.

Widths. (13)
C Day and night.

useful for monitoring operations on Installation Requirements

reversible or contraflow lanes.
One advantage of using non-intrusive
Applications detectors is ease of installation. This is
especially true if the detectors can be
The most common applications of mounted on existing structures, such as the
microwave radar detectors are to measure following:
vehicle speeds, and in some applications to
provide volume counts. As mentioned C Bridges.
above, advanced units that are available can
be used as presence detectors. In addition, C Luminaire poles.

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Manual TABLE OF CONTENTS Module 3. TABLE OF CONTENTS

C Sign structures. C Difficulties of maintaining alignment on

vibrating structures.
Radar detectors can be mounted in either the
side-fire position (see figure 3-11) or the C Inconsistent beam patterns caused by
overhead position (see figure 3-12). Setup changes in infrared energy levels due to
of the detector is simple and involves simply passing clouds, shadows, fog, and
aiming the unit at the traffic flow. Unlike precipitation.
other detection systems, most current radar
units do not require setup, configuration, or C Lenses used in some devices may be
calibration to provide accurate data.(13) sensitive to moisture, dust, or other
contaminants.
Maintenance costs of radar detectors have
also proven to be relatively low. One study C Inconsistent reliability under high volume
conducted in a northern State showed only a conditions.
2 percent failure rate for radar detectors over
2 years. This compares with a 34 percent An advantage of active infrared detectors is
failure rate of loop detectors over a 5-year the very narrow beam width that they emit.
period.(13) Costs are also kept lower, This allows for accurate determination of the
because maintenance of the detectors spatial position of a vehicle on a road. In
typically does not require lane closure on the addition, the profile of a vehicle can be
freeway. measured to within a few centimeters for
some systems.(22)
Infrared
Passive. Passive infrared detectors (see
Characteristics figure 3-14) do not transmit energy
themselves, but measure the amount of
There are two types of infrared detectors: energy that is emitted by objects in the field
of view. The amount of energy that is
C Active. emitted by an object depends on its surface
temperature, size, and structure, but not on
C Passive. its color or the surrounding lighting
conditions. For years, these detectors have
Active. Active infrared detectors (see figure been used as motion detectors; however,
3-13) operate by directing a narrow beam of detectors are currently available for
energy toward a background, such as the detecting presence as well.(14) As with active
surface of a roadway, at a certain pulse rate. infrared detectors, the ability of passive
A portion of the beam is directed back to the sensors to detect vehicles can be affected by
sensor, and vehicles are detected by changes environmental effects, such as fog and
in the characteristics of the infrared beam. precipitation, that can scatter and emit
The infrared beam can be transmitted from energy of their own. (18)
one side of the road to the other, or from an
overhead or roadside position to a device in Applications
the pavement surface. Disadvantages of
active infrared sensors include the Active. Currently available active infrared
following:(3) detectors can provide speed, count, density,
and vehicle classification. Accuracy is based

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Figure 3-11. Detector in Side-Fire Position. (21)

Figure 3-12. Detector in Overhead Position. (19)

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Figure 3-13. Active Infrared Detector. (11)

on the pulse rate, scan rate, and speed of the vehicle (see figure 3-15). If the beam is
vehicle. Faster pulse rates and scan rates scanned across the roadway at a fast enough
improve the accuracy of the system up to a pulse rate, a very accurate profile of a
certain point.(22) vehicle can be obtained. The vehicle may
then be classified by using an algorithm to
The presence of a moving or stationary compare the vehicle’s profile against defined
vehicle is determined by measuring the profiles for various vehicle classifications. (22)
round-trip propagation time of an infrared
pulse. This time will be shorter when a Passive. Passive infrared detectors can
vehicle is present. Speeds are measured by provide volume counts as well as presence
using two fixed beams, one slightly ahead of detection. Using a multichannel presence
the other. By comparing the times at which detector, passive infrared detectors can be
the front of a vehicle passed through each
made to mimic the pattern of an inductive
beam, the speeds can be determined.(22)
presence loop, and can replace
(14)
malfunctioning loop detectors.
One system that is coming onto the market
can determine vehicle classification by
Installation Requirements
measuring the profile of a vehicle. A two-
dimensional profile of a vehicle passing For speed measurement and presence
through the infrared beam is obtained by detection, infrared detectors may be installed
measuring the distance from the detector to
in either the side-fire or overhead position.

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Figure 3-14. Passive Infrared Detector. (11)

Scanning Infrared
Beams

Figure 3-15. Active Infrared Detector Measuring Vehicle

Classification. (23)

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In order to obtain vehicle classification, the The development of ultrasonic devices for
detector must be mounted in the overhead vehicle detection began in the mid-1950s.
position. Active infrared detectors are Michigan, Illinois, New York, and California
suitable for single lane detection, but can be were among the early users of ultrasonic
used only at short ranges. Passive infrared detectors in the 1960s. The use of these
detectors offer lane discrimination at long detectors was abandoned for the most part
range, but have relatively slow response because of the problems experienced.
time. (14) Recently, however, there have been efforts
to improve ultrasonic vehicle detectors.
Some currently available active infrared Results from these efforts continue to show
systems have incorporated microcontrollers promise.(11)
that offer continuous built-in testing. For
these systems, all adjustments to the system Disadvantages of current ultrasonic vehicle
are automatically performed, and no initial detection systems include the following:(3)
calibration is required during installation. In
addition, maintenance or design changes may C Environmental conditions (such as
be performed by uploading the system’s temperature, humidity, and air
program code, thereby, eliminating the need turbulence) can affect operations
to remove the detector from the mount.(22) because the detectors use sound waves
that propagate through the air.
Ultrasonic
C Surface of a vehicle may affect the
Characteristics performance of the detector. For
example, porous or textured surfaces
Ultrasonic detectors use electronic sound (e.g. snow on a vehicle) produce weaker
wave signals and a receiving unit to detect reflected sound waves.
vehicles traveling in a traffic stream. These
detectors operate on the same principle as C Speed is not measured directly.
microwave radar detectors in that both
transmit a beam into an area and receive the C Systems require a high level of special
reflected beam to detect a vehicle. (11) Similar maintenance capability.
to radar detectors, ultrasonic detectors
operate using the following waveforms:(22) Applications

C Continuous. Ultrasonic detectors can be used for both

presence and pulse applications. Using
C Pulse. signal processing techniques, the reflected
waves may be converted into volume, speed,
For a continuous waveform, a continuous and occupancy measures. In addition, some
signal is emitted, and vehicle presence is detectors can be used for presence detection
measured using the Doppler principle. This and vehicle classification. Vehicles are
form can be used to detect volume, classified by comparing the sonic signature
occupancy, and speed. For pulse waveform, created by a vehicle with a set of pre-
the detector operates by pulse allowing the programmed signatures of vehicles of
measurement of classification, as well as various classes.(22)
volume and presence.

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Installation Requirements

Ultrasonic detectors can be mounted in

either the side-fire or overhead position.
Detectors can provide either single lane or
multi-lane coverage. An example of an
ultrasonic detector installation is shown in
figure 3-16.

Acoustic

Characteristics

Acoustic detectors are completely passive

devices. Vehicles are detected by using
microphones along with signal processing
technology to listen for sounds associated
with vehicles. The acoustic technology used
by these detectors was originally developed
for military defense purposes, such as
tracking enemy submarines. The use of this
Figure 3-16. Example of Ultrasonic
acoustic technology for vehicle detection
Detector Installation. (11)
purposes has emerged within the last few
years. The advantages of acoustic detectors
are that they work well in all lighting
conditions and in wide temperature and distance from the sensors, the sound arrives
humidity extremes. (22) at both microphones almost simultaneously.
When the vehicle passes under the sensors,
Applications the sound reaches the lower microphone
first. By plotting time delay versus time, the
Acoustic detectors can be used to measure relationship can be used to estimate speed
volume, occupancy, and presence. Vehicle (see figure 3-18).(24)
classification can also be determined by
comparing the sonic signature of a vehicle to Installation Requirements
pre-programmed sonic signatures of vehicles
for various classes. (22) Acoustic detectors can be mounted either on
the side of the roadway or in an overhead
Speed can be measured by using an array of position. The detectors can monitor one or
microphones as shown in figure 3-17. The many lanes. Multilane detectors cannot
configuration shown in this figure consists distinguish between lanes, and may
of two microphones, one mounted above the experience interference among vehicles in
other. The concept behind this configuration different lanes. Single lane detection is
is that the time delay of sound arrival will be accomplished using directional microphones;
different for the upper and lower however, this increases the complexity and
microphones. This difference in time delay cost of the system. (24)
will vary as a vehicle approaches the sensors.
For example, when the vehicle is a certain

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T1(t)

T2(t)

Figure 3-17. Acoustic Detector.

1400
Time Delay, T2(t) - T1(t)

1200

Speed
1000 Determines
Shape
800

600

400

200

0
0 5 10 15 20

Time

Figure 3-18. Time Delay Versus Time Curve.

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Video Image Processing Tripline. These first generation systems are

the least demanding in terms of computer
Characteristics power and speed. Most of the VIP systems
that are commercially available at this time
An emerging technology that appears to be are of this class. Tripline systems operate by
very promising for meeting future data allowing the user to define a limited number
collection and surveillance needs is known as of detection zones in the field of view of the
video image processing (VIP). VIP systems video camera. When a vehicle enters one of
detect vehicles by monitoring specific points these detection zones, it is identified in a
in the video image of a traffic scene to manner analogous to that of inductive loops.
determine changes between successive In fact, tripline systems are the functional
frames.(25) The components of a VIP system equivalent of inductive loops and are
are shown in figure 3-19. Most systems intended to replace inductive loops in areas
consist of the following major elements: where a large number of loops are employed.
Limitations of tripline systems include the
C One or more video cameras. following:

C Microprocessor-based system for C Difficulty in detection due to the

processing the video image. presence of shadows or light changing
conditions.
C Software for interpreting the processed
images as vehicle detections. C Problems of occlusion (vehicle hidden by
another vehicle or object).
The microprocessor-based system receives
video inputs from the cameras. After Closed Loop Tracking. These systems are
receiving video input, the processor analyzes second generation VIP systems. They are an
the variation of gray levels in a series of extension of the tripline approach in that
pixels from the video image. The processor detection is performed using the same type
must filter out gray level variations resulting of detection zones. Closed loop tracking
from weather conditions, shadows, and day- systems represent the first attempt to
or night-time-related aspects. The resulting perform vehicle tracking. These systems
image consists of a blank background have the same problems as tripline systems
containing only identified objects such as with shadows and occlusion. They provide
vehicles, motorcycles, and/or bicycles. By more traffic flow information than tripline
analyzing successive video frames, the systems, but the complexity of both
system is able to calculate vehicle-related hardware and software subsystems is
information.(20) significantly greater than for tripline systems.

Classes of VIP Systems. VIP systems have Data Association Tracking. These systems,
evolved through the following three classes: commonly used in satellite surveillance
systems, are third generation VIP systems.
C Tripline. A basic requirement for these systems is the
capability to identify and track a
C Closed Loop Tracking. distinguishable object as it passes through
the field of view of the camera. In this
C Data Association Tracking. mode, the computer identifies vehicles by

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Figure 3-19. Components of Video Image Processing System. (11)

searching for connected areas of pixels that VIP Detector Performance. Factors
indicate motion when compared with the influencing detector performance include the
background information. A series of such following:(20)
vehicle detection is then associated to
produce tracking data for each vehicle. C Type of image being processed (i.e.,
upstream or downstream image).
Data association tracking systems require
less processing power than closed loop C Mounting height of the video camera
tracking systems, because they do not have (affects occlusion of vehicles).
to operate at the frame rate of the camera. C Number of lanes being processed.
They also offer better performance with
regard to shadows and occlusion. Shadows C Stability of video camera with respect to
are addressed using image analysis. wind and vibration.
Observed differences in the geometry of the
image reduce the effects of occlusion. A C Inclement weather, shadows, and poor
greater reliance on software sophistication lighting.
may reduce the hardware costs for these
systems. An additional advantage of these In most instances, the factors that affect VIP
systems is that a series of video cameras can detection capability the most are shadows
be used to cover a wide area, and a vehicle and reduced visibility due to inclement
can be “handed off” and tracked from one weather and poor lighting on detection
sensor to another as it passes from one field capability. As discussed above, a VIP
of view to another. system detects vehicles by analyzing changes
in pixels. Therefore, it may be difficult to

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differentiate between vehicles and changing Advantages of VIP Systems. The purpose
light conditions in all situations.(16) of the Oakland County project was to
implement an Advanced Traffic Management
During the implementation of a VIP system System (ATMS), which included installing
at signalized intersections in Oakland AutoScope VIP systems at 90 signalized
County, Michigan, the effects of shadows intersections. After 1.5 years of operation,
and lighting were minimized by improving several benefits of VIP over inductive loop
the detection algorithms.(16) This detectors were noted:(16)
improvement made it possible to distinguish
the direction a vehicle enters a detector, C Life cycle cost of video detection is
thereby, eliminating false detections due to lower than when using conventional
“wrong-way” entries. Typical causes of loops for a typical situation.
wrong-way entries include the following:
C Visual inspection of detection
C Shadows from vehicles in adjacent lanes. performance allows for detector size and
placement optimization.
C Light reflections (day or night) from
other objects. C Installation requires less set up time and
fewer pieces of equipment.
C Vehicles that enter the detection zone
from the wrong direction. C Installation and maintenance can be done
year-round, and require minimal traffic
An evaluation of the system during various disruption.
environmental conditions revealed both
improvements in the detection accuracy and C Relocation or addition of detector
reductions in false detections.(16) Table 3-11 regions can be done with software,
presents the results from that evaluation. resulting in no disruption to traffic.

Table 3-11. Results from Oakland County Evaluation of VIP System.

Environmental Conditions Detection Accuracy (%) False Detection Rate (%)

High Winds, Shadows 98.1 3.0
Overcast Skies, Snow, Wind 99.6 4.2
Overcast Skies, Wet Road, Wind 96.1 2.0
Day/Night Transition 97.1 7.4
Night 98.1 6.1
Partial Cloudiness, Light Wind 96.2 4.1

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C Detection is unaffected by resurfacing or time. Using a video monitor, detection lines

construction projects. are placed in the field of view by means of a
mouse or keyboard (see figure 3-20).
Additional advantages of a VIP system Different detector sizes and locations can be
include the following:(16) selected. Vehicles are detected when they
cross a detection line.(11)
C Camera pointing is easily done and
verified by a portable video monitor or The processing system of a tripline VIP
hand-held viewer. system provides outputs comparable to those
provided by loop detectors. These outputs
C Camera location is very flexible, include presence and passage as well as
allowing mounting on existing speed. From these measurements, other
structures. traffic parameters can be extracted, including
volume and occupancy. Similar to loop
C Installation of VIP system requires detectors, speed trap detectors can extract
minimal training. vehicle speed and vehicle classifications as
defined by length.(4) An advantage of VIP
C Detector layout can be done either in the systems is that a single camera can replace
field or in the office. many loops, offering true wide-area
detection.(11)
CCTV Applications. Closed-circuit
television (CCTV) cameras can be equipped For the more sophisticated systems in which
with VIP capability to give operators the vehicles are tracked, vehicle location
added capability to immediately verify and travel time through the detection zone
incident warning messages. If an incident may be obtained, as well as a higher level of
has occurred, operators may switch the VIP accuracy in vehicle speed and vehicle length.
from the video imagery mode to a standard Detector lines and speed traps are not
CCTV mode and monitor nearby incidents needed with these systems. Instead, vehicles
via pan/tilt/zoom controls. Once the camera are tracked frame-by-frame through the
viewing field has been modified, the VIP’s entire field of view. The time and distance
preset detection zones are lost and must be traveled between successive video frames is
reset prior to switching back to the video known, thereby providing an accurate
imagery monitoring mode. In the past, measurement of speed.(28)
resetting the detection zones has been a
cumbersome task; however, several VIP VIP systems are also very effective in
manufacturers have stated that this problem incident detection. For tripline systems,
is being solved.(26) incident detection algorithms similar to those
used for loop detectors may be used. A
Applications video tracking system can provide traffic
information to automatic incident detection
Currently available VIP systems can detect systems, and can often implement these
traffic at a number of locations within the algorithms directly with the same hardware
camera’s field of view. The detector platform. Since all vehicles are tracked with
locations are specified with interactive video this system, parameters pertaining to each
graphics and can be easily changed at any vehicle are known.(28)

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Figure 3-20. Identification of Detection Lines in Field of View.

Installation Requirements COMPARISON OF EMBEDDED AND

NON-INTRUSIVE DETECTORS
The video detection system includes the
following elements: A summary of the advantages and
disadvantages of each of the systems
C Roadside cameras. discussed was given toward the beginning of
this section (see table 3-10). Table 3-12 lists
C Video processor. the functional capabilities of the various
systems, as well as estimated installation and
C Appropriate software. detector costs. These estimates will vary by
manufacturer and quantity purchased.
The cameras are mounted above the
roadway, typically on existing poles, bridges, VEHICLE PROBES
or other structures. Occlusion caused by
other vehicles or objects can be minimized With the recent advances in computer,
by selecting proper camera location and communications, and vehicle locating
defining optimal detector sizing.(28) technologies, the vehicle itself can become
an important surveillance tool for monitoring
Some existing VIP systems offer complete traffic conditions in the roadway network.
fail-safe operation. For example, each Vehicles, acting as moving sensors (or
camera is monitored for video signal quality probes), can provide information about
and picture usability. If a camera fails, the traffic conditions on each link traversed.
affected detection zones will be switched to This information can be transmitted to a
a user-defined mode, such as “always on.” central computer system where it can then be
The nature of the problem is also reported to merged with information from other sources
operators in the traffic control center.(28) to provide an accurate representation of
actual travel conditions in the transportation

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Table 3-12. Characteristics of Traffic Detectors.

Applications Lane Communi- Cost

Coverage cation
Count Presence Speed Occup- Classifi- per Bandwidth Life Reliability Technology Detector
Detector
ancy cation Sensor Install (each)

Inductive Loop X X X X X Size of Low Moderate Moderate Current Moderate Low

loop ($1,000) ($500-
$800)
Magnetometer X X (1) X Single Low Long High Current Moderate Low -
lane ($1,000) Moderate
($500 -
$1500)
Microwave X (2) X (2) (2) Multiple Moderate Long High Current Low Low -
Radar ($500) Moderate
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($700 -
$3,000)
Infrared X X X X (2) Single Low - Long High Developing Low Moderate -
(active); Moderate ($500) High
Multiple ($1,000-

Module 3. TABLE OF CONTENTS

(passive) $8,000)
Ultrasonic X X X X (2) Single Low Moderate High Developing Low Low -
($500) Moderate
($600 -
$1,500)
Acoustic X X X X (2) Multiple Low - N/A N/A Developing Low Moderate
Moderate ($500) ($1,500)
Video Image X X X X X Multiple Moderate - Moderate Moderate Developing Low Very High
Processing High ($500) ($10,000 -
$25,000)

(1) Speed can be calculated by spacing sensors a known distance apart.

Manual TABLE OF CONTENTS Module 3. TABLE OF CONTENTS

system. Advantages of vehicle probes are or she passes through a toll plaza. Because
that the following measurements can tolls are collected automatically, the vehicle
typically be obtained: can pass through the toll plaza without
stopping.
C Link speeds.
AVI technology may also be used as a means
C Link travel times. of automatically collecting travel time
information along freeways. In Houston,
C Origin and destination of vehicle Texas, AVI systems have been installed to
traveling through system. monitor traffic operations on the main lanes
and the high-occupancy vehicle (HOV) lanes
Types of Vehicle Probes on three major freeways. Vehicles equipped
with transponders are used as probes to
Emerging technologies that utilize vehicles collect current travel time information. This
as probes include the following: information is used to alert freeway
operators to potential incidents and
C Automatic Vehicle Identification (AVI). congestion on both the main lanes and the
HOV facilities. (29)
C Automatic Vehicle Locating (AVL).
The original AVI technology, which has
C Cellular Telephone Probes. been in use for several years, uses a radio
frequency signal from the roadside to
Automatic Vehicle Identification (AVI) activate a transponder located in the vehicle.
Transponders can be classified according to
AVI systems permit individual vehicles to be the type of source required to power the
uniquely identified as they pass through a transponder and the degree to which the
detection area. Although there are several transponder can be programmed.
different types of AVI systems, they all
operate using the same general principles. A Classes of transponders, based on type of
roadside communication unit broadcasts an power source, include the following:(30)
interrogation signal from its antenna. When
an AVI-equipped vehicle comes within range C Active.
of the antenna, a transponder (or tag) in the
vehicle returns that vehicle’s identification C Passive.
number to the roadside unit. The
information is then transmitted to a central C Semi-Active.
computer where it is processed. In most
systems, the transponder and reader/antenna Active. With active transponders, power to
technology are independent of the computer the transponder is supplied from either an
system used to manage and process the internal battery or a connection to the
vehicle identification information.(3) vehicle’s power supply. The transponder is
activated by an interrogation signal from the
Currently, the most common application of roadside communication unit. It responds to
AVI technology is for automatically the signal by broadcasting its own signal
collecting tolls on tollways. In this (which contains the identification number for
application, toll charges are electronically the vehicle) from an internal transmitter.
deducted from the driver’s account when he This type of transponder generally has a

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greater operating range and is more reliable facility or by the agency issuing the
than other types of transponders. The life transponder; however, they cannot by
expectancy of an active transponder is reprogrammed without returning the
between 7 and 10 years. transponder to the manufacturer.

Passive. With passive systems, the Type II. These transponders have
transponder does not require any internal or read/write capability. In these transponders,
external power supply. Instead, the some of the memory contains permanent
interrogation signal from the antenna is information (such as vehicle identification
modulated and reflected to the reader. number) and cannot be reprogrammed.
Because the return signal is weaker, passive However, additional memory can be
systems typically produce less lane-to-lane provided and may be reprogrammed or
interference than active systems. The weak written remotely from the reader. This type
return signal, however, causes passive of transponder is typically used in toll
transponder systems to have shorter systems to record time, date, location, and
operating distances. Due to the simplicity of account balance for vehicles.
their circuitry, passive transponders have a
life expectancy of approximately 40 years. Type III. These transponders are also
known as “smart cards.” They have
Semi-Active. Semi-active transponders use extended memory and are capable of full
an operating approach similar to that of two-way communication. With this system,
passive transponders in that they are vehicles can be warned of incidents,
activated only after an interrogation signal is congestion, or adverse weather conditions,
received from the reader. Unlike passive enabling drivers to take alternative routes.
transponders, however, semi-active This type of system requires sophisticated
transponders use an internal power to boost technology for both the roadside and
the return signal to the reader. This vehicle-based equipment.(4)
increases the reading distance of the
transponder. Like active transponders, a Automatic Vehicle Location (AVL)
semi-active transponder has a life expectancy
of approximately 7 to 10 years. AVL systems enable the approximate
location of a vehicle to be determined and
Classes of transponders, based on the degree tracked as it traverses the transportation
to which they can be programmed, include network. These systems have many uses for
the following:(25) many different customers, including the
following:(31)
C Type I.
C Emergency Services - aid in dispatching
C Type II. emergency vehicles.

C Type III. C Transit Agencies - track vehicles and

provide passengers with arrival time
Type I. Type I transponders are read-only estimations through information displays.
tags that contain fixed data, such as a vehicle
identification number. They can initially be C Delivery Companies - plan the most
programmed either at the manufacturing efficient dispatch of fleet vehicles.

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C Private Citizens - allow instant dispatch positional accuracy of dead-reckoning and

of tow truck in the event of a vehicle map-matching, most AVL systems use more
breakdown or to recover a stolen advanced technology options.
vehicle.
Signpost. When vehicles, such as transit
This technology can also be used to buses, regularly travel a fixed route, many
determine the severity of congestion or the fleet operators have found that signpost-
occurrence of an incident, by obtaining based positioning systems offer an
probe reports from vehicles traveling in the alternative to more advanced AVL
network. Software in a control center can technologies. Antennas are placed at
automatically monitor travel speeds and locations throughout the vehicle’s route and
transit times of vehicles equipped with AVL record the time when the vehicle passes
technology. nearby. A signpost-based AVL system can
also be a valuable extension of systems
There are numerous techniques and intended for other purposes. Reader
technologies than can be used for locating antennas that communicate with vehicle tags
the vehicle, including the following:(31) for electronic toll collection can also track
the location of vehicles from one toll booth
C Dead-Reckoning and Map-Matching. to another. The Harris County Toll
Authority in Houston and the Illinois Toll
C Signpost. Authority in Chicago are currently using
such systems.
C Ground-Based Radio Navigation.
Ground-Based Radio-Navigation. In
C Loran-C. “terrestrial” or “ground-based” radio-
navigation, the AVL vendor sets up several
C Global Positioning Systems (GPS). receiving antennas in a metropolitan area.
Each appropriately equipped vehicle
C Differential GPS. broadcasts a radio frequency (RF) signal to
all nearby receiving antennas. By measuring
Dead-Reckoning and Map-Matching. the time it takes for the signal to travel to the
Dead-reckoning systems monitor the antenna, the distance from the vehicle to the
vehicle’s internal compass and odometer and antennas can be determined. If the vehicle’s
calculate its position by measuring its signal was received by three or more
distance and direction from a known central antennas, the vehicle’s position can be
starting point. Dead-reckoning systems uniquely determined. A disadvantage of
frequently get off track and can be corrected radio-navigation is that RF signals have
using a technique called map-matching. difficulty transmitting through large
Map-matching systems store a map of the obstructions, such as mountains, tunnels,
vehicle’s coverage area in a database and parking garages, and metropolitan canyons
assume that when a vehicle changes formed by the large buildings that line many
direction, it must have turned from one road downtown city streets.
on to another. When a vehicle does make a
turn, map-matching systems alter the Ground-based radio-navigation systems are
vehicle’s record location to the nearest among the most inexpensive AVL systems
possible point at which the turn could have for the user. However, since constructing
taken place. Because of the low degree of

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the necessary infrastructure requires receivers in the same locale, virtually

significant financial investment on the part of eliminating all errors in measurements.
the AVL vendor, these systems are usually
available only in dense metropolitan areas Cellular Telephones
with large market potential.
Using radio frequency receivers and
LORAN-C. LORAN-C is similar to triangulation techniques, it is possible to
ground-based radio navigation, except that it determine a vehicle’s location by measuring
uses a communication system set up by the signals resulting from cellular phone usage
U.S. Government. Uncertainty about the within the vehicle. In conjunction with map-
government’s future plans for this system matching algorithms, vehicles (cellular
have lead to a decrease in the number of probes) can be tracked as they traverse area
commercial AVL systems using LORAN-C. freeways. The ability to track vehicles via
In addition, LORAN-C communication cellular telephones allows vehicle speeds, as
signals often experience errors due to well as travel times for various freeway
atmospheric conditions. segments to be measured. With so many
cellular telephones currently in operation,
Global Positioning System. Global this system has a potential to provide an
positioning systems (GPS) use a network of inexpensive source of traffic surveillance.(31)
24 satellites that are continuously orbiting
the Earth to locate any object anywhere on A test project was conducted in the
the planet. The satellites are available free- Washington, DC, area to test the feasibility
of-charge to anyone with a device capable of using cellular probes to obtain real-time
of receiving the satellite signals. The U.S. travel information.(32) The surveillance
Department of Defense (DOD) launched the system was based on passive geolocations
satellites in order to track objects of interest (only vehicles that have initiated a call will
on the ground. The position of the objects is be used for the period during which the call
determined measuring how long a radio is active). This method typically provides a
signal takes to reach the object from multiple sufficient probe population, since cellular
satellites. GPS is by far the most accurate phone usage is directly correlated with traffic
global navigation system ever devised, with congestion.
accuracies in the range of 5 to 30 meters.
Similar to radio-navigation, GPS signals The cellular surveillance system consists of
have difficulty transmitting through large two basic components:
objects. The signals also have trouble
transmitting through opaque objects, such as C Geolocation control system (GCS).
leaves on trees.
C Traffic information center (TIC).
Differential GPS. Differential GPS is a
technique used to improve the accuracy of At the GCS, a direction finding system
standard GPS. With differential GPS, a (consisting of a series of towers) is used to
receiver placed at a known location provide latitudes and longitudes of cellular
calculates the combined error in the satellite probes. This information is sent to the TIC,
range data. By knowing the error, where information on traffic conditions is
correction factors can be applied to all other derived from a series of probes. Traffic
information is then disseminated to the users
(e.g., operators at control center).

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When an initiated call is detected by the C Cellular telephones.

GCS, the following information is collected
and sent to the TIC: C Freeway service patrols.

C Time. C Call boxes.

C Probe ID number (randomized to ensure Mobile reports are most often used for
privacy). incident detection. A survey of existing
freeway management systems around the
C Latitude and longitude. United States revealed that a significant
portion of incidents are detected either
C Information as to whether a key number through service patrols or cellular calls.(33)
(such as 911) was called. Frequently, mobile reports help detect
incidents faster than many methods of
C Information on whether the probe was automatic incident detection.(34)
within the boundary of interest.
Cellular Telephones
C Confidence factor associated with the
accuracy of the latitude and longitude. This method of quick detection is becoming
more of a resource as the number of cellular
If the message is within bounds, the TIC telephones on the roadways continues to
uses the position to determine which traffic increase. Some traffic management systems
link the probe is traveling on. If a key have established free cellular call numbers
number is used, the TIC requests additional for reporting incidents or requesting aid.
information from vehicles within a certain These toll free numbers connect the caller
distance of the call. Once it has been directly to the traffic management center or
verified that the requested probes are on the to other agencies responsible for responding
traffic link in question, speeds are calculated. to incidents. Numbers that are easy to
The TIC keeps historical information on remember (such as 999 or CALLMAP)
speed profiles for various traffic links by should be used to help these systems be
time-of-day. Incoming speeds are compared effective. It is estimated that half of all
with these historical files. If the difference incidents are reported via cellular telephones.
between current speed and historical speed Other advantages of this system include the
exceeds a set threshold value, a potential following:(3)
incident flag is set. Data from additional
probes is then requested by the GCS. If the C Low start-up costs.
threshold value is exceeded a certain number
of times, an incident is posted. C Two-way communication between caller
and response agency.
MOBILE REPORTS
The effectiveness of this method of incident
Potential freeway surveillance techniques detection depends on the number of cellular
that should not be overlooked are those telephones on the roadway and the
classified as mobile reports. Examples of willingness of drivers to report incidents. To
mobile report methods include the following: increase effectiveness, a campaign to inform
drivers about the cellular call-in system and

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the benefits of reporting an incident is Call Boxes/Emergency Telephones

recommended.(3)
Call boxes or emergency telephones may
Freeway Service Patrols also be used to detect incidents or to locate
motorists in need of help. These devices are
Another effective method for monitoring located on the side of the freeway (see figure
traffic conditions and detecting incidents is 3-22) and are typically spaced from 0.40 km
freeway service patrols. A freeway service to 0.80 km (0.25 to 0.50 mi) apart.(3)
patrol consists of a team of trained drivers Motorists can stop and use these devices to
who cover a particular area of freeway, report a problem.
monitoring traffic operations. Many
different vehicles are used for freeway Using emergency telephones, motorists can
service patrols around the United States, contact a dispatcher to report conditions and
including light trucks, mini-vans, and tow request help. With call boxes, motorists
trucks. An example of a patrol vehicle and simply press certain buttons to request
equipment used by the Illinois State various services (such as police, fire, or
Department of Transportation is illustrated ambulance). Because there are no voice
in figure 3-21. The most noticeable benefits transmissions with call boxes, they are
of service patrols are those involving relatively inexpensive to install as compared
incident management.(35) Typical objectives to telephones. However, emergency
of a service patrol include the following:(36) telephones result in fewer false alarms and
greater likelihood that the appropriate
C Helping stranded motorists. services will be provided.(3)

C Locating incidents, clearing them, and CLOSED-CIRCUIT TELEVISION

contacting the appropriate agency. (CCTV)

C Providing assistance at major incidents. Closed circuit television (CCTV) systems

have been used for many years to provide
C Providing traffic reports to particular visual surveillance of the freeway system.(1)
agencies. Control centers typically use CCTV systems
for the following purposes:
Freeway service patrols have the benefit of
not only being able to detect an incident, but C Detection and verification of incidents.
also to assist travelers and remove vehicles
upon detecting them. By performing the C Monitoring traffic conditions.
entire incident management process on their
own, service patrols greatly reduce the time C Monitoring incident clearance.
to remove an incident which, in turn,
minimizes negative effects on traffic The discussion in this section will address
operations. The operations of service two types of CCTV systems:
patrols are covered more extensively in
Module 8. C Fixed location.

C Portable.

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Figure 3-21. Illinois DOT’s Advanced Technology Quick-Tow

Incident Response Vehicle with Equipment.

Fixed Location C Communication system connecting

camera to control center.
For fixed location CCTV systems, video
cameras are permanently mounted either on C Video monitors and camera controls
existing structures along the freeway or on located in control center.
specially installed camera poles (see
figure 3-23). This type of system consists of CCTV systems allow control room
various components, including the personnel to visually monitor sections of
following:(39) roadway and to react directly to the actual
conditions on the roadway. Since operators
C Video camera unit. can lose interest if required to constantly
view CCTV monitors, and may fail to notice
C Mounting structure (existing or incidents immediately after they occur,
installed). current systems are being designed to
automatically position cameras at suspected
C Controller cabinet housing the control incident locations (as signaled by incident
equipment. detection algorithms) and to alert the
operator.(26)

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Figure 3-23. Fixed-Location Closed-

Circuit Television Camera. (16)

Video images from cameras may be

transmitted to a control center using one of
the following video transmission types:

C Full motion video.

C Compressed video.

Full Motion Video

Using full motion video, real-time video is

transmitted to the control center. Real-time
video is typically transmitted at a rate of 30
frames per second. This transmission type
results in no information loss; however, it
requires a wide communication bandwidth,
such as that provided by coaxial cable or
fiber optic cable. (3)

Compressed Video

When it is not feasible to install the

communication medium required for full
Figure 3-22. Call Box. (38) motion video, compressed video offers an
attractive alternative. An advantage of
compressed video transmission is that video
data can be transmitted over conventional
telephone lines and cellular channels. (3)

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With compressed video techniques, C Camera mounted on a pan-and-tilt unit.

transmission rates of 8 to 10 frames per
second are possible. Because some C Telescopic boom.
information is lost between pictures frames,
the resulting image appears slightly “jerky”. C Television monitor.
The image, however, is adequate for
monitoring freeway operations.(27) C Video recorder.

A compressed video system typically C Camera control unit for controlling pan,
includes the following: tilt, and zoom functions.

C Compression and decompression C Generator for powering equipment.

computer (standard industrial PC) for
each camera/monitor link. C Air compressor for operating telescopic
boom.
C Appropriate software.
Video transmission can be accomplished
C Communications medium (typically a using the same techniques available for fixed
leased ISDN [Integrated Service Digital location CCTV systems. A system used in
Network] line). Dallas, Texas, consists of portable
surveillance trailers with the ability to
Standard cameras, monitors, and control transmit video images over temporary
hardware can be used, and therefore, can be telephone lines.(26) A system in Los Angeles,
reused if the communications medium is California uses a video van that is capable of
upgraded to allow for full motion video transmitting full motion video back to the
transmission.(26) control center via wireless
communication.(39)
Portable
SUMMARY OF TRAFFIC
Portable CCTV systems can serve several SURVEILLANCE APPLICATIONS
purposes including the following:(39)
Table 3-13 summarizes the traffic
C Short term traffic monitoring in areas surveillance technologies discussed and
with non-recurring congestion (e.g., particular applications for which they are
work zone, critical incident, etc.). best suited. The recommendations shown in
this table are not meant to imply that other
C Traffic monitoring at special traffic detection methods cannot be used; rather,
generators (e.g., stadiums, parades, etc.). the table shows which technologies currently
work best for specific applications.
C Determination of optimum camera However, it should be taken into
location for fixed location CCTV consideration that as technological
systems. improvements are made, the applications of
certain technologies will be expanded.
Portable CCTV systems are typically
mounted in a light truck or van or on a
trailer (see figure 3-24). Components of a
portable system include the following:(40)

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(17)
Figure 3-24. Portable Closed-Circuit Television System.

The factors used to assign the technologies C Response times.

to certain applications were detector
performance and reliability. Cost was not C Staffing levels.
taken into consideration. As technology
continues to improve, detectors that are C Anti-icing material.
currently not cost feasible will become more
competitive. Other areas where environmental detectors
are used are in tunnels. In these areas,
ENVIRONMENTAL DETECTORS special sensors are needed to monitor the
level of noxious fumes, such as carbon
Environmental detectors on freeways are monoxide. The sensors are typically used to
used to detect adverse weather conditions control the ventilation systems in tunnels.
such as ice. These systems alert motorists to
dangerous conditions and in some situations Freeways
inform maintenance personnel so that
evasive actions may be taken. An early There are a number of commercially
warning system for detecting icy conditions available systems for monitoring
on certain freeway sections can reduce the environmental conditions on freeways.
following:(4) These systems can be used to warn drivers

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Table 3-13. Traffic Surveillance Applications.

Infrared Video CCTV

Monitoring Inductive Magneto- Microwave Ultrasonic Acoustic Image Vehicle Mobile
Application Loop meter Radar Active Passive Processing Fixed Portable Probes Reports

Incident Detection
X X X X X

Incident Removal
X X

Traffic Conditions
X X X X X X X X X X X
3-63

Special Event
X X X X X X X X X

Implement Control
X X X X X X X X X X
Strategies

Module 3. TABLE OF CONTENTS

Maintenance Activity
X X X X X X X X X X X X

Vehicle Classification
X X X

Ramp Metering
X X
Manual TABLE OF CONTENTS Module 3. TABLE OF CONTENTS

of potentially dangerous driving conditions.

In addition, the information can be used by
operators in traffic management centers to
do the following:(40)

C Control dynamic message signs.

C Decide whether to close roads.

C Integrate weather information into

incident detection algorithms.

There are several environmental sensors

available today. Categories of environmental
sensors include the following:(40)

C Road condition sensors - measure

surface temperature, wetness or dryness,
presence of snow, and surface moisture
conductivity.

C Visibility sensors - detect presence of

fog, smog, heavy rain, snow, or
sandstorms.

C Thermal mapping - detects presence of

ice.
Figure 3-25. Roadside Environmental
Figure 3-25 shows a roadside environmental Monitoring System. (41)
monitoring system that is capable of
measuring visibility and precipitation. C Air temperature, humidity, and dew
point.
Several manufacturers also produce
complete weather stations. An example of C Wind speed and direction.
such a system is the SCAN (Surface
Condition Analyzer) developed in the United The system consists of sensors the size of
States. SCAN is able to monitor pavement hockey pucks that are embedded in the
and environmental conditions and provide pavement. Capacitors within the sensors
the following information:(42) measure electrical charges from water, snow,
ice, or chemicals. Thermostats are used to
C Pavement temperature. measure surface temperatures. SCAN
systems are currently used in 48 States and
C Presence of water, ice, snow, or in 8 countries.(41)
chemicals on pavement.

C Precipitation.

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Tunnels C Responds to changing technologies and

transportation system demands.
Monitoring systems in tunnels are used to
limit the build-up of noxious fumes from The ability of agencies to effectively operate
vehicle exhausts. Output from the monitors and maintain a freeway management system
is used to perform the following functions: is vital to the success of the system.(6) This
section discusses issues associated with the
C Control tunnel ventilation. operations and maintenance of surveillance
systems.
C Warn drivers of poor visibility.
Operations
C Set safe speed limits within the tunnel.
Operations includes those tasks involved in
Most systems monitor the level of noxious the day-to-day function of a system. The
gases and visibility by using infrared primary responsibility of personnel in charge
absorption techniques. A gas monitoring of operating a surveillance system is to
system typically consists of the following: monitor freeway conditions. Freeway
monitoring may serve several purposes,
C Infrared transmitter and receiver. including the following:

C Electronic signal processing unit. C Monitoring traffic operations.

Outputs from the monitors are sent to the C Detecting incidents.

system controlling tunnel ventilation. Tunnel
ventilation becomes more cost effective C Monitoring incidence clearance.
when operated in conjunction with a
monitoring system. Cost savings arise from C Monitoring environmental conditions.
reduced frequency of operation and
maintenance of the ventilation system.(43) C Supporting the implementation of
There are currently many systems available control strategies.
for monitoring air quality within a tunnel;
however, it is important that a monitoring Operators may monitor freeway conditions
system be reliable, accurate, and able to by using any of the following devices:
operate with minimal maintenance.(44)
C Displays or printouts showing conditions
3.4 LESSONS LEARNED either graphically or in a tabular format.

OPERATIONS AND MAINTENANCE C Closed-circuit television systems.

Effective operations and maintenance of a C Mobile reports.

traffic management system are required to
ensure that the system meets certain Additional tasks with which an operator may
objectives, such as the following: be involved include the following:(4, 6)

C Continuously accomplishes the goals and C Controlling and managing equipment and
objectives for which it was designed. ensuring continuity of operation.

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C Monitoring system performance criteria. C Address maintenance needs (e.g.,

maintenance requirements, maintenance
C Updating system databases. costs, personnel requirements) during
the planning process.
C Notifying maintenance personnel of
system malfunctions. C Ensure that required budget and staffing
needs can be met.
C Communicating with transportation and
emergency response agencies. C Perform cost tradeoff analyses during the
design phase to identify techniques for
C Documenting daily operational functions reducing maintenance requirements.
and events such as incident occurrences,
equipment failures and repairs, and C Consider that complex surveillance
changes in software and hardware technologies require higher personnel
components. skill levels to maintain.

Maintenance C Ensure that maintenance personnel

receive adequate training.
Proper design and installation techniques are
important to ensure the success of a system. C Keep accurate records of maintenance
Maintenance, however, is also a critical task activities to aid in predicting future
that must be considered if the system is maintenance needs and in analyzing
going to operate as intended. Maintenance costs.
activities can be grouped into three
categories:(4) Operations and Maintenance Costs

C Remedial. The success of a system begins with the type

and quality of the equipment being utilized.
C Preventive. Budgetary and funding problems that traffic
agencies typically face may result in the
C Modification. selection of equipment mainly on the basis of
initial start-up cost, rather than on lifetime
Remedial maintenance is necessitated by cost. Consequently, less expensive
malfunctions and equipment failures, and equipment is purchased during the
usually demands emergency repair to restore installation process. However, this is not
operations. Preventive maintenance includes always the most cost-effective solution. (11)
work done at scheduled intervals to Therefore, operations and maintenance costs
minimize equipment failure. Modification should be considered together with start-up
involves replacing equipment and usually costs during the equipment selection
results from equipment design flaws or process.
required upgrades to improve system
performance. All three maintenance A Texas Department of Transportation
categories should be considered in (TxDOT) research project established
determining budget requirements. guidelines for estimating operations and
maintenance costs.(6) The cost estimates
For a maintenance program to be successful, were based on the following sources:
the following factors should be considered:(4)

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C TxDOT metropolitan districts with through State and local maintenance

substantial ITS deployment. budgets. These funds are often insufficient
because of competition with other
C ITE report, Operation and Maintenance maintenance functions. Therefore, it is
of Electronic Traffic Control Systems. important that continued funding for
operations and maintenance be addressed in
C FHWA report, Cost Estimates and the planning stage.
Assumptions for Core Infrastructure.
PRIVACY CONCERNS
C Texas municipalities and transit agencies.
Most surveillance technologies have little
C Technical journals. impact on privacy, because there is no need
for vehicle identification. Privacy, however,
C Equipment suppliers. is a critical concern when using technologies
that identify vehicles, such as AVI, AVL,
Table 3-14 shows the operations and and cellular telephone tracking. Privacy is
maintenance cost estimates for a surveillance also a concern with the use of closed-circuit
system. This table lists the estimated unit television.
operations cost, estimated unit maintenance
cost, combined operations and maintenance A survey of drivers in the United States
cost, and the assumptions related to factors showed that in 1978, 67 percent of people
included in each of the costs. Using were concerned about privacy. Results from
quantities measured in terms of the base 1994 showed that the percentage had
units shown in the table, total operations and climbed to 84 percent, revealing that privacy
maintenance costs can be determined. Note is a major concern for drivers.(45)
that the estimated maintenance costs include
maintenance personnel costs, while the Although some people may not mind if their
estimated operations costs do not included vehicles alone are identified, many fear that
personnel costs. surveillance from different sources (e.g.,
credit card purchases, phone calls, travel
Most of the operations and maintenance habits, etc.) could be combined to build a
costs in table 3-14 are given as ranges in detailed personal profile of their lifestyles.
order to allow for adjustments for the The ability to compile information about an
following factors: individual’s travel patterns, toll payments,
and other activities creates the potential for
C Age and quality of equipment. a database that has not previously existed.
Due to advances in computer technology,
C Personnel skill levels. this kind of information is highly
transportable, and opportunities exist for
C System designs. inappropriate access to and use of this
personal information.(46)
In many situations, outside financing sources
are more readily available for the It must be taken into account that privacy is
development and construction of new one of the goals against which any system’s
systems than for operating and maintaining effectiveness may be measured. For
the systems once they are built. Operating example, one of the first AVI tolling systems
and maintenance costs are typically funded

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Table 3-14. Estimated Operating and Maintenance Costs for Surveillance Systems.(6)

Estimated Estimated Estimated

Annual Annual Annual
Description Base Unit Operations Maintenance Combined Cost Assumptions
Cost/Unit Cost/Unit O&M
Costs/Unit

CCTV each $0 $500 - $1300 $500 - $1300 Costs include routine maintenance for CCTV
cameras, as well as the camera controls, housing,
and/or support pole.

CCTV Cameras w/ Video each $0 $700 - $1800 $700 - $1800 Costs include routine maintenance for CCTV
Image Processing Capability cameras, as well as camera controls, housing,
and/or support pole, and VIP calibrations.
3-68

Imbedded Detectors:

Inductive Loop per station $0 $200 - $300 $200 - $300 Costs include contract maintenance/replacement of
loops. Costs assume four lanes per station, with
two loops per lane. Costs also assume loop failure
rates of 4% to 6% per year.

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Non-Intrusive Detectors:

Radar, Ultrasonic, per station $0 $200 - $300 $200 - $300 Costs include routine maintenance of detectors.
Acoustic, Infrared Costs assume four lanes per station, with one
detector per lane.

Video Image Processing per station $0 $500 $500 Costs include routine maintenance and calibration
of detectors. Costs assume one video detector per
station.
 Manual TABLE OF CONTENTS
Table 3-14. Estimated Operating and Maintenance Costs for Surveillance Systems (cont.).(6)

Estimated Estimated Estimated

Annual Annual Annual
Description Base Unit Operations Maintenance Combined Cost Assumptions
Cost/Unit Cost/Unit O&M
Costs/Unit

AVI:

Transponders each $0 $10 - $15 $10 - $15 Costs include routine maintenance and
replacement of transponders.

Readers per station $0 $500 $500 Costs include routine maintenance.

3-69

AVL:

Leased Transceivers/ per vehicle $750 - $1200 $0 $750 - $1200 Operations costs include the lease cost of the
Antennae transceivers and antennae, and the associated
communications cellular air time charges;

Module 3. TABLE OF CONTENTS

maintenance is provided by the
transceiver/antennae provider.

Owned Transceivers/ per vehicle $250 - $500 $100 - $200 $350 - $700 Operations costs include communications cellular
Antennae air time charges; maintenance costs include routine
maintenance and replacement of transceivers and
antennae.
Manual TABLE OF CONTENTS Module 3. TABLE OF CONTENTS

to be implemented was in Hong Kong in and maintenance procedures. The following

1983. Each month, drivers using the discussion presents recommendations for the
electronic tolling system were sent spacing and placement of mainline traffic
statements that contained itemized accounts detectors and CCTV cameras.
of where they had driven and when. The
drivers didn’t like the idea of a government Mainline Traffic Detectors
agency tracking their daily highway travel;
therefore, the system was removed two Spacing
years after it was introduced, despite the fact
that the technology worked.(46) For reasons For monitoring traffic conditions and
like these, it is very important to design any incident detection, detectors should be
surveillance with privacy in mind. placed along the freeway and on ramps to
detect changes in traffic conditions.
Fortunately, it is relatively easy to design Guidelines for detector spacings are as
most surveillance systems with privacy in follows:(3,4)
mind.(45) For example, AVI systems can be
designed to assign vehicles a random C Typical mainline detector spacings range
identification number for monitoring between 0.40 and 0.80 km (0.25 and 0.5
purposes, in which case the identification of mi).
the driver is never made. This same process
can be used with AVL and cellular-based C Spacings over 0.8 km (0.5 mi) are
traffic surveillance systems.(32) inadequate for incident detection
purposes.
In general, consumers may be willing to give
up a certain degree of privacy if they feel C Spacings below 0.4 km (0.25 mi)
that the benefits will outweigh the risks (as generally produce little or no increase in
in the case of credit card use). It is therefore effectiveness.
important that the public be informed about
the benefits of using certain surveillance C Tunnels or covered roadway sections are
technologies. The key to overcoming exceptions, and may require spacings of
privacy concerns is to inform the public less than 0.4 km (0.25 mi).
about what information is being collected
and how the data will be used.(47) C Minimally, at least one traffic detector
station should be provided between
SPACING AND PLACEMENT ISSUES interchanges or freeway ramps, with
maximum spacings of 1.6 to 2.4 km (1.0
Selecting the location of detectors is an to 1.5 mi).
important step in the implementation of a
surveillance system. Spacing and placement C Detectors are also typically placed
affect both the cost and performance of the before and after freeway bottlenecks
system. The detectors should be placed (e.g., entrance ramps, lane closures, etc.)
close enough together to provide adequate and metered entrance ramps.
surveillance of the system, but as the spacing
decreases, the cost of the system increases. Placement
In addition, it is desirable to place the
detectors in a location that will result in As discussed earlier, most existing traffic
minimum delay to traffic during installation detectors can be classified as either

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embedded or non-intrusive. An embedded C Ongoing maintenance costs may be

detector system consists of sensors in or minimal.
below the surface of the roadway. Non-
intrusive detectors are mounted on a CCTV Cameras
structure above the surface of the pavement.
The primary objective of a CCTV system is
The following issues associated with to provide visual monitoring of freeway
installing and maintaining embedded conditions and to verify incidents. The
detectors: California Department of Transportation,
District 7, has developed guidelines for
C Installation typically requires drilling into CCTV camera site selection.(39,48,49) The
or cutting the pavement. following is a summary of these
recommendations.
C Embedded detectors usually have higher
installation costs than non-intrusive Site Selection Criteria
detectors.
Most cameras with a standard 10-to-1 zoom
C Installation may require lane closure, have a viewing range of 0.8 km (0.5 mi) in
which results in delay to vehicles. all directions. Full freeway coverage would
therefore require a maximum camera spacing
C When feasible, embedded detectors of 1.6 km (1 mi). Full coverage of all
should be installed during the freeways, however, is frequently cost
construction or rehabilitation of a prohibitive. Therefore, proper camera site
freeway to avoid delays to traffic. selection becomes a critical factor. Factors
that should be considered in the selection of
C Because modifications to the pavement a camera site include:
structure are required for the installation,
deterioration of the road surface is C Surveillance of congested freeway
escalated; therefore, there are further sections to provide maximum visibility
ongoing maintenance costs associated and coverage of weaving and merging
with replacing damaged detectors or areas near ramps and interchanges.
repairing degraded road surfaces.
C Ability to provide a clear view of areas
Non-Intrusive Detectors with high accident frequencies (based on
accident data).
Issues associated with installing and
maintaining non-intrusive detectors include C Ability to provide suitable access for
the following: maintenance personnel based on the
geometric layout of the area.
C Can typically be installed and maintained
without disrupting traffic. C Minimal obstruction to view caused by
landscaping, billboards, freeway signs, or
C Installation costs are significantly topography.
reduced when an existing mounting
structure can be used. C Ability to verify messages of variable
message signs.

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C Ability to effectively address power, with standard 10-to-1 zoom and a viewing
communication, and underground utility range of 0.8 km (0.5 mi), video surveillance
considerations. can be provided for a 1.6 km (1 mi) freeway
section (assuming no blockage due to
C Ability to provide suitable access to the horizontal or vertical curves).
proposed communication system.
The next step in the preliminary site selection
Candidate sites for CCTV systems may be process is to perform a field check. The
prioritized on the basis of accident frequency objectives of the field check are to verify the
(high, medium, and low). Threshold values following:
to classify accident frequencies should be
based on local conditions. Areas with high C Veiling range at “ground eye level.”
accident frequencies will require video
surveillance to expedite incident detection C Geometric layout.
and clearance. Areas with medium and low
accident frequencies may also require video C Maintenance access.
surveillance. Site selections for these
locations will be based on local criteria, such C Power and utility concerns.
as the importance of a particular freeway
section. In addition, video surveillance may While in the field, each preliminary site
be used to monitor ramps and freeway selected should be marked so that the site is
sections near heavy traffic generators (e.g., easily identifiable for the final site selection
stadiums) during special events. process.

Preliminary Site Selection Final Site Selection

Preliminary site selection should be based on The purpose of the final task is to perform a
the criteria discussed above. These sites video survey to verify camera viewing
should be noted on a scaled base map, along ranges and select correct mounting heights.
with the following characteristics of the For high-speed freeway sections, a mobile
freeway: CCTV camera system is recommended.

C Accident frequencies plotted over 0.4 Following are considerations for selecting
km (0.25 mi) intervals. mounting heights:

C Strategic roadway infrastructure. C Mounting heights on poles generally

vary from 6.0 to 13.7 m (20 to 45 ft).
C Locations of variable message signs.
C Heights below 6.0 m (20 ft) may be
C Locations of underground high-risk susceptible to vandalism.
utility lines.
C Pole heights above 13.7 m (45 ft) may
Cameras should be located in the vicinity of result in maintenance problems and
high-accident frequency areas and near safety hazards.
variable message signs and other strategic
areas. Areas with high-risk utility lines
should be avoided if possible. For cameras

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C Lower heights (between 6.0 and 9.1 m how to use the software to the City of Miami
[20 and 30 ft]) are preferred when it is for 112 days at a nominal cost.
necessary to look beneath overpasses. The City of Miami was responsible for
recruiting 25 volunteer drivers willing to
C Cameras at heights below 10.7 m (35 ft) have their vehicles equipped with
can be accessed by a small bucket truck. transponders. Many of the drivers recruited
commuted from the periphery of the city to
C Cameras at heights between 10.7 and downtown, and this provided coverage for 5
13.7 m (35 and 45 ft) would require a of the 17 corridors in the peak direction
larger hoist truck. during the peak period. Installation of the
transponders for each vehicle took about one
When possible, cameras should be mounted hour. A single AVL unit consisted of a
directly on existing structures. This will control unit (about the size of a video tape
result in a significant reduction in the initial cassette) and a “pancake” antenna.
installation costs.
AirTouch Teletrac provided training on the
3.5 EXAMPLES use of the software to CUTR researchers
and the City of Miami Planning staff and
MIAMI AUTOMATIC VEHICLE then provided a workstation, which was a
LOCATION (AVL) (32) Compaq 386 computer with an internal high-
speed modem. The city provided a
The City of Miami, Florida, needed an dedicated phone line for communication
accurate, inexpensive method of collecting between the workstation and AirTouch
average travel speed data in order to Teletrac’s operations center in Fort
calculate roadway level of service as Lauderdale. (AirTouch Teletrac maintains a
required by the 1985 Florida Growth network of 27 receiving antennas throughout
Management Act. In 1988, the City of Dade, Broward, and Palm Beach counties in
Miami staff determined that automatic South Florida. RF signals from the receiving
vehicle location (AVL) technology could be antennas are transmitted to AirTouch
used to measure speeds on specific Teletrac’s operations center in Fort
corridors. (AVL is a means of continuously Lauderdale.)
monitoring the location of vehicles in a road
network. Vehicles are equipped with a The software was configured to poll each of
transponder device that transmits a radio- the 25 vehicles’ positions every 30 seconds
frequency (RF) signal to a central location at when the vehicle ignition was on and every
regular intervals.) In 1993, the City of 5 minutes when the vehicle ignition was off.
Miami contracted with the Center for Urban Each time a vehicle’s position was recorded,
Transportation Research (CUTR) to set up the following information was obtained:
a field operational test of AVL to measure vehicle number, speed, time, date, and
vehicle operating speeds on 17 location. Data were recorded for the
transportation corridors in the city. CUTR following time periods:
recruited AirTouch Teletrac to serve as the
vendor for the AVL system. AirTouch C Weekday mornings, 5 a.m. to 10 a.m.
Teletrac agreed to provide 25 transponders,
one workstation, one copy of its C Weekday afternoons, 3 p.m. to 8 p.m.
FleetDirector™ software, and training on
C Saturdays, 10 a.m. to 2 p.m.

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Data were gathered for 112 days, and data with the capability of identifying tagged
for over 4400 vehicle trips were obtained. vehicles at periodic intervals along the
CUTR staff wrote two software programs to roadway.
analyze vehicle-location data and report
average speed. In order to determine the TRANSCOM is an umbrella organization
accuracy of the calculations for average trip serving the New York/New Jersey
speeds, CUTR researchers also set up a metropolitan area in coordinating and
process to compare observed values with disseminating transportation information. In
calculated values for the average speed over 1991, TRANSCOM retained a team led by
a vehicle trip. Method 1 yielded a ± 8.3 PB Farradyne, Inc., to establish the
percent accuracy, and Method 2 yielded a ± feasibility of using ETTM equipment for
7.1 percent accuracy. Since Method 2 was traffic surveillance and incident detection
more accurate, it was used in compiling the applications. The project was called
output. TRANSMIT (TRANSCOM’s System for
Managing Incidents and Traffic) and was
CUTR has demonstrated that the AirTouch divided into two phases. The first phase
Teletrac automatic vehicle location system concentrated on evaluating the use of ETTM
can be used to measure average vehicle technology for traffic surveillance and on
operating speeds on Miami’s 17 developing a preliminary design of a traffic
transportation corridors in the peak direction surveillance system for an ETTM incident
during the peak period, given sufficient detection system. The second phase
electronic storage capacity, appropriate data included the final design and construction of
analysis software, and volunteer drivers. the initial stage of the system as an 28.8-km
This system could be used anywhere in the (18-mi) operational field test along sections
six metropolitan areas where AirTouch of the New York State Thruway and the
Teletrac is available. However, in order to Garden State Parkway. The primary
conduct this experiment outside of those six objective of the TRANSMIT project was to
areas, an AVL vendor would have to be process available traffic flow data for early
enlisted. detection of incidents and abnormal traffic
congestion.
TRANSCOM ELECTRONIC TOLL
AND TRAFFIC MANAGEMENT An analysis was conducted to determine the
(ETTM)(50,51) reader antenna spacing and toll tag
penetration necessary to detect an incident
ETTM, or electronic toll and traffic within five minutes with a false alarm rate of
management, has seen rapid growth. two percent or less. The analysis used the
Currently, more than 20 agencies in 8 following roadway classes: arterial, two-lane
countries have installed a system and are highway, and three- to four-lane highway.
collecting tolls automatically. Another 23 The results indicated that the arterial
agencies in 7 countries are in the process of roadway class would result in the longest
testing, studying, or implementing automatic detection time. The analysis concluded that
toll collection. ETTM systems have the the five-minute detection time could be
potential to be used for other ITS achieved if the following percentages of
applications that could include congestion equipped vehicles were provided:
pricing, advanced payment systems, traveler
information, and traffic management. C Two-lane highways: 0.9 percent.
ETTM requires the installation of readers

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C Three- and four-lane highways: 2.1 instrument the metropolitan freeway system
percent. in Houston with an automatic vehicle
identification (AVI) system to monitor traffic
C Arterials: 7.6 percent. conditions. The AVI system was designed
to provide travel time information on about
An 28.8-km (18-mi) corridor along the New 120 miles of freeways and 100 miles of
York State Thruway in Westchester and reversible high-occupancy vehicle (HOV)
Rockland Counties and the Garden State lanes.
Parkway in Bergen County were defined for
an operational field test. Twenty-two The initial planning began in 1991. The
ETTM sites were constructed, and existing North Houston Corridor, with three parallel
overhead sign structures and overpasses radial freeways, was selected as the study
were used for the placement of reader site. This corridor had several favorable
antennas. New structures were built where characteristics: one toll facility with available
existing structures were not available. capacity; one freeway with heavy congestion
because of inadequate capacity and
The incident detection algorithm developed reconstruction activities; and one freeway
by PB Farradyne, Inc., determines the with moderate congestion and an HOV lane.
probability of an incident when tagged The corridor also served the Houston
vehicles detected at an upstream reader are Intercontinental Airport, the central business
not detected at the downstream reader district, and other major activity centers. A
within the expected arrival time. The later a demonstration project was designed using
vehicle is, the higher the probability of an cellular telephones for the collection of
incident. traffic condition information. This project
recruited 200 volunteers who commuted to
At the time this project was designed, the and from work using one of the three
technology for Electronic Toll Collection freeway routes. The demonstration project
(ETC) in the Greater New York/New Jersey was conducted for about 18 months, during
Metropolitan Area was undetermined, so it which time a more permanent and automated
was decided that the ETTM antennas and system for traffic monitoring was being
reader cabinet equipment would be leased, developed using AVI technology. The
not purchased. Therefore, if the traffic demonstration project was a success in that
surveillance concept is found to be valid, useful real-time travel time information
successful and is expanded throughout the was collected and made available to the
region, the equipment can be made public in a variety of ways.
compatible with the regional ETC equipment
from which the tag population originates. CONNECTICUT MICROWAVE
The construction cost estimate for the RADAR (13)
operational field test was $1,195,600, which
included equipment leasing costs for a 24- The Connecticut Department of
month period. Transportation (ConnDOT) chose radar
detection for the recent design of their
HOUSTON AUTOMATIC freeway surveillance system. Connecticut
(52)
VEHICLE IDENTIFICATION (AVI) has two separate systems operating within
the State. The first system is a federal
The Texas Department of Transportation demonstration project covering
awarded the first of three contracts to approximately 19 km (12 mi) of Interstates

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I-84 and I-91 in the Hartford area, and it is detectors and installation configurations to
the first surveillance system in the country to determine the detector accuracy. The
utilize radar as an incident detection difference between vehicle and detected
technology. Because of the early success in speed ranges from 4 km/h (2.5 mi/h) for the
Hartford, radar detection is also being used narrow beam detector, to 5.6 ki/h (3.5 mi/h)
in the design of the I-95 Freeway for the wide beam detector in a side-fire
Management System. The I-95 system is configuration, and up to 10 mi/h for the long
installed along the southern coast of range detector. The errors associated with
Connecticut, covering 90 km (56 mi) from the long range detector can be attributed to
the New York State border east to Branford. the operating principle and placement of the
Both systems rely on speed data being sent detector. The detector operation is based on
back from the radar detectors to monitor the Doppler principle: it is most accurate
traffic flow condition and to detect incidents. when it is aimed directly at the traffic flow.

Three different types of radar detectors are Testing and day-to-day operations have
being used on the projects: wide beam shown that the radar detectors are highly
detectors, narrow beam detectors, and long accurate during varying traffic and weather
range detectors. The Radar detectors for the conditions. The degree of reliability and
Hartford Area ATMS (44 individual accuracy demonstrated by the detectors has
detectors) have been installed for 2 years. allowed ConnDOT engineers to be confident
During this time, only one detector has in the data displayed. With the use of the
failed, and the others have survived harsh video cameras that are also part of the
winters with record snowfalls and system, ConnDOT engineers have been able
significantly below-average cold to detect and verify incidents that would
temperatures. In addition to their reliable otherwise have been unknown to them, and
operation, the radar detectors have proven to initiate a timely response. Lessons
to be easily installed and setup. learned from the Connecticut system have
been applied in the development of systems
The detectors have been installed for only a in Maryland, New Jersey, Massachusetts,
few years, but the data looks promising. and Georgia.
Testing has been performed for the various

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