Traffic Safety

Fundamentals Handbook

Minnesota Department of Transportation

Office of Traffic, Safety and Technology
Published August 2008
Prepared by CH2M HILL, Inc.

Mn/DOT Traffic Safety Fundamentals Handbook Introduction

The Minnesota Department of Transportation (Mn/DOT) published the original version of the Traffic Safety Fundamentals Handbook in April, 2001.
Over 2,000 copies have since been distributed through Mn/DOTs education and outreach efforts to practicing professionals in both government
agencies and the private sector. In addition, this handbook has been used as a resource in undergraduate and graduate traffic engineering classes at
the University of Minnesota.
In the years since 2001, the field of traffic safety has witnessed several important changes. First, Federal Highway Legislation (SAFETEA-LU) raised
the level of importance of highway safety by making it a separate and distinct program and by increasing the level of funding dedicated to safety.
In response to this legislation, the Federal Highway Administration (FHWA) provided implementation guidelines that required the states to prepare
Strategic Highway Safety Plans and encouraged their safety investments to be focused on low cost stand-alone projects that can be proactively
deployed across both state and local highway systems.
Minnesotas Strategic Highway Safety Plan (SHSP) was prepared in accordance with the FHWA guidelines and was approved in July, 2006. The SHSP
included identification of a statewide safety goal, safety emphasis areas and a list of high priority safety strategies. The SHSP also identified a new
approach to distributing the funds associated with the Highway Safety Improvement Program driven by the distribution of fatal and life changing
injury crashes across Minnesota. As a result of this strategic safety planning effort and the hard work of safety professionals in both State and local

governments, dozens of highly effective safety projects have been implemented and the results are
impressive Minnesota met the initial safety goal of getting under 500 traffic fatalities (494 fatalities
in 2005).
However, one fact remains constant highway traffic fatalities are still the leading cause of death
for Minnesotans under 35 years of age. This indicates there is still much work to do in order to move
Minnesota Toward Zero Deaths.
This new edition of the handbook has been updated to reflect new safety practices, policies and
research and is divided into four sections:

Crash Characteristics national and state crash totals including the basic characteristics as a
function of roadway classification, intersection control, roadway design and access density.

Safety Improvement Process Black Spot Analysis + Systematic Analysis = Comprehensive Safety
Improvement Process.

Traffic Safety Toolbox identification of safety strategies with an emphasis on effectiveness.

Lessons Learned

For additional information regarding traffic safety, please contact Mn/DOTs Office of Traffic, Safety
and Technology, Traffic Safety Engineer at (651) 234-7016.

Document Information and Disclaimer:

Prepared by: CH2MHILL, Inc
Authors: Howard Preston, PE, Michael Barry and William Stein, PE
Funding: Provided by Mn/DOT Division of State Aid for Local Transportation
Published by: Mn/DOT Office of Traffic, Safety and Technology
The contents of this handbook reflect the views of the authors who are responsible for the facts and accuracy of
the data presented. The contents do not necessarily reflect the views of or policies of the Minnesota Department of
Transportation at the time of publication. This handbook does not constitute a standard, specification or regulation.

Table of Contents
Crash Characteristics
A-1
A-2
A-3
A-4
A-5
A-6
A-7
A-8
A-9
A-10
A-11
A-12
A-13
A-14
A-15
A-16
A-17
A-18

Nationwide Historic Crash Trends

Upper Midwest 2006 Crash Data
Fatality Rates of Surrounding States2006
Minnesota Urban vs. Rural Crash Comparison
AASHTOs Strategic Highway Safety Plan
Role of Driver, Road, and Vehicle
Emergency Response Time
Fatal Crashes are Different
Minnesotas Crash Mapping Analysis Tool (MnCMAT)
Minnesotas Crash Mapping Analysis Tool (MnCMAT)
Crash Involvement by Age and Gender
Total Crashes by Road, Weather, & Lighting Conditions
Access vs. Mobility The Functional Class Concept
Typical Functionally Classified Urban System
Intersection Crash Rates (MN) by Control Type and Family
Intersection Crash Severity (MN) by Control Type and Family
Intersection Crash Distribution by Rural vs. Urban
Roadway Segment Crash and Fatality Rates by
Jurisdictional Class
A-19 Roadway Segment Crash Rates of Facility Type by
Rural vs. Urban
A-20 Roadway Segment Crash Distribution by Rural vs. Urban
A-21 Roadway Segment Crash Rates as a Function of Facility Type
and Access Density (MN)

Safety Improvement Process

B-1
B-2
B-3
B-4
B-5
B-6

B-7
B-8
B-9
B-10
B-11
B-12
B-13
B-14
B-15

Minnesotas Strategic Highway Safety Plan (SHSP)

Minnesotas Safety Emphasis Areas
Safety Emphasis AreasGreater Minnesota vs. Metro
Comprehensive Safety Improvement Process
Why Have a Black Spot Identification Process?
Alternative Methods for Identifying Potentially
Hazardous Locations
Effect of Random Distribution of Crashes
Calculating Crash Rates
Supplemental Analysis: More Detailed Record Review
Mn/DOTs High CrashCost Trunk Highway Intersections
Systematic Analysis State Highways
Implementation Guidance for State Highways
Systematic AnalysisCounty Highways
Implementation Guidance for County Highways
Safety Planning at the Local Level

Traffic Safety Tool Box

C-1
C-2
C-3
C-4
C-5
C-6
C-7
C-8
C-9
C-10
C-11
C-12
C-13
C-14
C-15
C-16
C-17
C-18
C-19
C-20
C-21
C-22
C-23
C-24
C-25
C-26
C-27
C-28
C-29
C-30
C-31
C-32
C-33

Traffic Safety Tool BoxThen vs. Now

Traffic Safety Tool BoxThen vs. Now
Effectiveness of Safety Strategies
Roadside Safety Strategies
Edge Treatments
Horizontal Curves
Slope Design/Clear Recovery Areas
Upgrade Roadside Hardware
Effectiveness of Roadside Safety Initiatives
Addressing Head-On Collisions
Intersection Safety Strategies
Conflict PointsTraditional Intersection Design
Conflict PointsNew Intersection Design
Enhanced Signs and Markings
Intersection Sight Distance
Turn Lane Designs
Roundabouts and Indirect Turns
Traffic Signal Operations
Red Light Enforcement
Safety Effects of Street Lighting at Rural Intersections
Flashing Beacons at Rural Intersections
Transverse Rumble Strips at Rural Intersections
Pedestrian Safety Strategies
Pedestrian Crash Rates vs. Crossing Features
Curb Extensions and Medians
Neighborhood Traffic Control Measures
Speed Zoning
Technology Applications
Work Zones
Crash Reduction Factors
Average Crash Costs
Crash Reduction Benefit/ Cost (B/C) Ratio Worksheet
Typical Benefit/Cost Ratios for Various Improvements

Lessons Learned
D-1
D-2
D-3

Lessons Learned: Crash Characteristics

Lessons Learned: Safety Improvement Process
Lessons Learned: Traffic Safety Tool Box

Crash CharacteristicsContents

A-1

Nationwide Historic Crash Trends

A-13 Access vs. Mobility The Functional Class Concept

A-2

Upper Midwest 2006 Crash Data

A-14 Typical Functionally Classified Urban System

A-3

Fatality Rates of Surrounding States2006

A-15 Intersection Crash Rates (MN) by Control Type and Family

A-4

Minnesota Urban vs. Rural Crash Comparison

A-16 Intersection Crash Severity (MN) by Control Type and Family

A-5

AASHTOs Strategic Highway Safety Plan

A-17 Intersection Crash Distribution by Rural vs. Urban

A-6

Role of Driver, Road, and Vehicle

A-7

Emergency Response Time Comparison

A-18 Roadway Segment Crash and Fatality Rates by

Jurisdictional Class

A-8

Fatal Crashes are Different

A-9

Minnesotas Crash Mapping Analysis Tool (MnCMAT)

A-10 Minnesotas Crash Mapping Analysis Tool (MnCMAT)

A-11 Crash Involvement by Age and Gender
A-12 Total Crashes by Road, Weather, & Lighting Conditions
Traffic Safety Fundamentals
Handbook2008

A-19 Roadway Segment Crash Rates of Facility Type by

Rural vs. Urban
A-20 Roadway Segment Crash Distribution by Rural vs. Urban
A-21 Roadway Segment Crash Rates as a Function of Facility Type

and Access Density (MN)

Nationwide Historic
Crash Trends
1972

1979

1984

1989

1994

1999

2004

2006

Crashes
Total (thousand)

N/A

N/A

N/A

6,700

6,500

6,300

6,181

5,973

Fatal (thousand)

N/A

N/A

N/A

41

36

37

38

39

Injury (thousand)

N/A

N/A

N/A

2,153

2,123

2,026

1,862

1,746

PDO (thousand)

N/A

N/A

N/A

4,459

4,337

4,226

4,281

4,189

54,589*

51,093

44,257

45,582

40,716

41,345

42,636

42,642

Registered Vehicles (million)

119

144

159

181

195

N/A

238

251

VMT (trillion)

1.3

1.5

1.7

2.1

2.4

2.7

3.0

3.0

Crashes/100 MVM

N/A

N/A

N/A

317

276

235

206

198

Fatalities/100 MVM

4.3

3.3

2.6

2.2

1.7

1.5

1.4

1.4

Fatalities per million registered vehicles

458

355

278

252

209

195

180

170

N/A

$19.4

N/A

N/A

$150.5

N/A

N/A

$230.6**

Fatalities
Total

Traffic
Rates

Costs
US Dollars (billion)
*1972 was the worst year for fatalities in U.S.
**Estimated for reported and unreported crashes in 2000

N/A = Not Available

PDO = Property Damage Only

VMT = Vehicle Miles Traveled

100 MVM = Hundred Million Vehicle Miles

Source: National Highway Traffic Safety Administration (NHTSA)

Highlights

Nationally, over the past 10 years, there have been about 6.5 million crashes and between 40,000 and 45,000 deaths annually.

Over that same period, VMT (exposure) has increased by almost 30%.

The long-term trend is fewer crashes and fatalities, in spite of the increased exposure.

As a result, there have been fairly dramatic decreases in both crash and fatality rates.

Even though there have been significant decreases in both total crashes and fatalities, there have been large increases in the costs of those crashes.

Traffic Safety Fundamentals

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A-1

Upper Midwest Area

2006 Crash Data
Highlights

Minnesota

North
Dakota

South
Dakota

Iowa

Wisconsin

Total

78,745

16,534

15,830

54,815

117,877

Fatal

456

101

172

386

659

Injury

24,663

4,141

4,296

16,950

35,296

PDO

53,626

12,292

11,362

37,479

81,922

494

111

191

439

712

Registered Vehicles (million)

4.8

N/A

1.0

3.4

5.3

VMT (billion)

56.6

7.7

8.5

31.7

59.4

Crashes/MVM

1.4

2.0

1.9

1.7

2.0

Fatalities/100 MVM

0.9

1.5

2.3

1.2

1.2

Fatalities/MRV

103

N/A

191

129

134

$1,529

$399

$411

N/A

$2,715

Crashes

Fatalities
Total

Regionally, there is a wide variation from state to state

in both the total number of crashes (15,000 to 118,000)
and the number of fatalities (111 to 712).

This variation is consistent with the state to state variation

in exposure (VMT).

Minnesota has averaged approximately 90,000 crashes

and between 500 and 600 fatalities annually over the
past several years.

The trend in Minnesota is fewer crashes and fatalities, in

spite of an increase in exposure (VMT).

Minnesota has been a leader in the area of highway

safety, with one of the lowest statewide average crash
and fatality rates compared to other states in both the
region and nationally.

There is a relationship between the number of fatal

crashes and fatalities. In general across the upper
midwest area, the ratio was 1.1 fatalities per fatal crash.

Traffic
Rates

Costs
US Dollars (million)

N/A = Not Available

PDO = Property Damage Only

VMT = Vehicle Miles Traveled

100 MVM = Hundred Million Vehicle Miles

MRV = Million Registered Vehicles

Source: 2006 State Publications of MN, ND, SD, IA and WI

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A-2

Fatality Rates of
Surrounding States2006
National Average =
1.4 Fatalities / 100 MVM

NORTH
DAKOTA

MINNESOTA

1.4

Minnesota has the lowest fatality rate in the region

and consistently one of the lowest fatality rates in the
nation.

National Fatality Rates

- Average 1.4
- Range 0.8 to 2.3
- Trends Lowest fatality rates in the northeast
(mostly urban)
- Highest rates in west, southwest, and southeast
(most rural)

Minnesota had the second lowest rate.

Since 1994, Minnesotas fatality rate has dropped by

almost 42%. This is the largest decline of any state.

Traffic fatalities are still the leading cause of death for

Minnesota residents under 35 years of age.

The data suggests there are significant opportunities

to move Toward Zero Deaths by focusing state safety
efforts on the primary factors associated with severe
crashessafety belts, alcohol, young drivers, road
edges, and intersections.

0.9

SOUTH
DAKOTA

WISCONSIN

1.2

2.1

MICHIGAN

1.0

IOWA

1.4

NEBRASKA
MnDOT_A-03_3

Highlights

1.4

ILLINOIS

1.2

Fatality Rate = Fatalities per Hundred

Million Vehicle Miles (MVM) Traveled

Minnesota

INDIANA

1.3

Nationally

Year

Fatalities

Fatality Rate

Fatality Rate

1984

584

1.8

2.6

1989

605

1.6

2.1

1994

644

1.5

1.7

1999

626

1.2

1.5

2006

494

0.9

1.4

Source: National Highway Traffic Safety Administration (NHTSA)

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Minnesota Urban vs. Rural

Crash Comparison
28% Rural

Highlights

Total Crashes
Fatal Crashes

72% Urban

he total number of crashes is typically a

T
function of exposure (VMT).

I n Minnesota, slightly more than one-half of the

VMT is in urban areas and approximately 70%
of the total number of statewide crashes are in
urban areas.

owever, 70% of the fatal crashes in Minnesota

H
are in the rural areas.

n the average, rural crashes tend to be more

O
severe than urban crashes the fatality rate on
rural roads is more than 2.5 times the rate in
urban areas.

The higher severity of rural crashes appears to

be related to crash type, speed, and access to
emergency services.

70% Rural
30% Urban

Miles

13% Urban
87% Rural

Vehicle Miles
Traveled (VMT)
48% Rural
52% Urban

Note: Rural Refers to a nonmunicipal area and cities with a

population less than 5,000.

Source: 2004 - 2006 Minnesota TIS Crash Data

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AASHTOs Strategic
Highway Safety Plan
Highlights

Persons Killed in Traffic Crashes

60000

1200
1060

42589

National

40000

900
42642
800

42013

44525

875

43510

777

39250

35000

615

644

650

538

558

25000

700

655

30000

510

568
494*

600
500

20000

400

15000

300

National

10000

200

Minnesota

5000
1965

1970

1975

100
1980

1985

1990

1995

2000

Year
*

AASHTOs Strategic Highway Safety Plan was first

published in 1997 and then updated in 2004.

The plan suggested a new national safety performance

measure the number of traffic fatalities and setting a
goal to reduce the nations highway fatality rate to not
more the one fatality per 100 million VMT by 2008.

he plan introduced innovative ideas including:

T
Shared responsibility all roads, all levels of road
authorities
Safety Emphasis Areas
Focus on Proven Strategies
Consideration of Driver,
Roadway and Vehicle
interactions when
analyzing crash causation
Development of
State and Local
Comprehensive
Safety Plans

1000

47087

980

45000

51093

1024

50000

In the 1990s, AASHTO concluded that historic efforts

to address traffic safety were not sufficient to cause
a continued decline in the annual number of traffic
fatalities.

1100

52627

2005

MnDOT_A-05_2

The 494 traffic fatalities in 2006 is the lowest number in more than 50 years.

Minnesota

55000

Source: Minnesota Department of Transportation (Mn/DOT) and National Highway Traffic Safety Administration (NHTSA)

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A-5

Role of Driver,
Road, and Vehicle
Crash Causation Factors

Highlights

Crashes are caused by a variety of factors involving

drivers, the roadway, and vehicles

Driver behaviors that attribute to crashes include

not wearing a safety belt, using alcohol, and
driving aggressively. Driver behaviors are a factor
in a total of 93% of crashes.

Roadway features focus on road edges and

intersections. Roadway features are a factor in
34% of crashes.

Vehicle equipment failures, including tire

blowouts, towing trailers, over size and load
distribution. Vehicle failures are a factor in 12%
of crashes.

Roadway
(34%)

- Road edge dropoffs

- Intersection design

3%

27%

57%

3%
6%
Vehicle
(12%)
- Tire blowouts 2%

Studies have shown that Safety Programs

that address multiple factors of the four
Safety Es Education, Enforcement,
Engineering, and Emergency Serviceswill
be the most effective.

Examples of education and enforcement programs

include the Department of Public Safetys Project
Night Cap (alcohol) and CLICK IT or Ticket (safety
belt usage).

- Towing trailers
- Oversize and load distribution

Mn

DO

T_

A-0
6_
3

1%

Driver
(93%)

ExampleRoadways are the sole contributing factor in 3% of crashes and

the roadway and driver interaction is the factor in 27% of crashes.

- Not wearing safety belt

- Using alcohol
- Driving aggressively

Source: Human Factors & Highway Safety, Elizabeth Alicandri

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Emergency Response
Time Comparison
Rural

Emergency Response Time Comparison

For Urban vs. Rural Areas

7 min.

Urban

Time of
Crash to
Notification
Time
3
min.

10 min.
Notification to
the Time of
Arrival
at Scene

5 min.

46
min.

29 min.
Arrival at Scene to Time
of Arrival at Hospital

21 min.

EMS Response Time (minutes)

Source: National Highway Traffic Safety Administration (NHTSA)

29 min.

Note:

Times are rounded to

nearest minute
Rural Refers to a
nonmunicipal area and
cities with a population
less than 5,000

Highlights

It appears that Emergency Response time may be a significant contributing factor to the higher frequency of fatal crashes in rural areas.

Response times in rural areas are more than 50% longer than in urban areas.

The higher frequency of fatal crashes in rural areas combined with the large EMS response times has lead to the research currently underway, in both Minnesota and
nationally, regarding an automatic emergency notification system (MayDay) and enhancing the 511 (roadway information) system to provide first responders with
real-time routing information to trauma centers

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A-7

Fatal Crashes
are Different
Highlights

40%

All Crashes
All Rural Crashes

34%

Fatal Crashes

32%

Percentage (%)

30%

28%

23%

20%

19%
17%
15%

15%

14%

10%
7%

Rear End

5%

4%

Run Off Road

Head-On

Angle

For the past 30 years, the primary safety performance

measure was the total number of crashes. This resulted
in safety investments being focused on locations with
the highest number of crashes, which also have larger
numbers of the most common types of crashes.
The most common types of crashes in Minnesota are Rear
End (28%) and Right Angle (19%). These crashes occur
most frequently at signalized intersections along urban/
suburban arterials which ended up being the focus of
safety investment.
One problem with directing safety investments towards
signalized urban/suburban intersections is that there was
little effect on reducing fatalities only about 10% of fatal
crashes occur at these locations.
The advent of Minnesotas Toward Zero Deaths (TZD)
program and the recent adoption of a fatality-based safety
performance measure lead to research that first identified
that fatal crashes are different than other less severe
crashes.
Fatal crashes are overrepresented in rural areas and on
the local road system. The most common types of fatal
crashes are Run Off Road (34%), Right Angle (23%), and
Head-On (17%).
These facts about fatal crashes have changed Mn/DOTs
safety investment strategies which are now focused on
road departures in rural areas and on local systems.

Source: 2004 - 2006 Minnesota TIS Crash Data

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A-8

Minnesotas Crash Mapping

Analysis Tool (MnCMAT)
Highlights

In order to assist cities and counties in gaining a better

understanding of crash characteristics on their systems, Minnesota
Local Road Research Board and Minnesota County Engineers
Association (MCEA) have made a new tool available the
Minnesota Crash Mapping Analysis Tool (MnCMAT).

MnCMAT is a mapbased computer application that provides 10

years of crash data for every county in Minnesota.

Individual crashes are spatially located by reference point along

all roadways in each county.

Up to 73 pieces of information are provided for each crash,

including route, location (reference point), date/day/time,
severity, vehicle actions, crash causation, weather, road
characteristics, and driver condition.

Analysts can select specific intersections or roadway segments for

study. An overview of the entire county can also be generated.

For more information about MnCMAT, consult the website:

http://www.dot.state.mn.us/stateaid/sa_crash_map_tool.html

MnCMAT(1 of 2)

Traffic Safety Fundamentals

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A-9

Minnesotas Crash Mapping

Analysis Tool (MnCMAT)
Highlights

The recommended analytical process

for conducting a safety/crash study is to
compare Actual conditions at a specific
location (intersection or segment of highway)
compared to Expected conditions (based on
documenting the average characteristics for a
large system of similar facilities).

MnCMAT supports this analytical process

by providing both the data for individual
locations and for larger systems individual
or multiple counties.

These graphs provide summaries of crash

data for the City of Brooklyn Park.

The data indicates crashes predominately

occur on dry surface conditions and are more
likely to occur during the week. Additionally,
the graph shows the distribution of crashes by
severity.

MnCMAT(2 of 2)

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A-10

Crash Involvement by
Age and Gender
Licensed vs. CrashInvolved Drivers, 2006

3500

Percentage of All Drivers in Population

1000

Age Group

85+

80-84

75-79

70-74

60-64

50-54

55-59

45-49

40-44

30-34

35-39

500

25-29

85-89

80-84

75-79

70-74

65-69

60-64

55-59

50-54

45-49

40-44

35-39

30-34

25-29

20-24

15-19

1500

20-24

2000

10-14

2500

15-19

Female

5-9

Percentage

10

3000

0-4

12

Male

Number of Persons Killed, 2006

Percentage of All Drivers in Crashes

14

65-69

16

Age Group

Source: 2004 - 2006 Minnesota Crash Facts

Highlights

The distribution of fatal crashes and total crashes by age indicates that young people are overrepresented.

A recent analysis of crashes found that Minnesota has the highest percentage of young drivers (under 19 years of age) involved in fatal crashes of any
state (approximately 14%), and those drivers only make up about 8% of the driving population.

Minnesotas Strategic Highway Safety Plan has documented that young drivers (under 21 years old) are involved in 24% of fatal crashes. As a result,
addressing young driver safety issues has been adopted as one of Minnesotas main safety emphasis areas.

One strategy has been found to be particularly effective at reducing the crash involvement rate of young drivers adoption of a comprehensive
Graduated Drivers License (GDL) program. The Minnesota Legislature took a step in this direction in 2008 by adding provisions that prohibit driving
between midnight and 5 a.m. during the first 6 months of licensure and limiting the number of unrelated teen passengers during the first 12 months of
licensure.

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Total Crashes by Road, Weather,

& Lighting Conditions
Highlights

Road Conditions

S ome elements of traffic safety are counterintuitive. Many people think that most crashes
occur at night during bad weather.

owever, the data clearly indicates that crash

H
frequency is a function of exposure. Most crashes
occur during the day on dry roads in good weather
conditions.

I t should be noted that some recent research has

looked at safety issues during night time hours and
during snow events. This research concludes that
these conditions represent a significant safety risk
because low level of exposure results in very high
crash rates.

In addition, the new focus on fatal crashes

reinforces the concern about night time hours
being more at risk11% of all crashes occur
during dark conditions but 26% of fatal crashes
occur during hours of darkness.

68% Dry
2% Other
7% Snow/Slush

14% Wet/Muddy
9% Ice or
Packed Snow

Weather Conditions
56% Clear
1% Fog, Dust,
Smoke, ect.
3% Other

26% Cloudy
14% Rain, Snow,
Sleet or Hail

Lighting Conditions
66% Daylight
16% Dark with
Streetlights
11% Dark without
Streetlights

5% Dawn or
Dusk
2% Other
MnD

OT_

A-11

_4

Source: 2004 - 2006 Minnesota TIS Crash Data

Traffic Safety Fundamentals

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A-12

Unrestricted

Access vs. Mobility

The Functional Class Concept
Highlights

Local R

oad

5%

Ro

ors
ect

ty

n
ou

s
ad

ll
Co

ets
tre
S
ds
ty d oa
Ci an ip R
sh
wn
o
T

One of the key concepts in transportation planning deals with the functional classification
of a road system. The basic premise is that there are two primary roadway functions
Access and Mobilityand that all roadways serve one function or the other, or in some
cases, both functions.

The four components of most functionally classified systems include Local Streets,
Collectors, Minor Arterials, and Principal Arterials.

he primary function of local streets is land access and the primary function of principal
T
arterials is moving traffic. Collectors and minor arterials are usually required to serve some
combination of both access and mobility functions.

ey reasons supporting the concept of a functionally classified system include the

K
following:
It is generally agreed that systems that include the appropriate balance of the four types
of roadways provide the greatest degree of safety and efficiency.
It takes a combination of various types of roadways to meet the needs of the various
land uses found in most urban areas around the state.
Most agencies could not afford a system made up entirely of principal arterials. A
region could be gridlocked if it was only served by a system of local streets.
Roadways that only serve one function are generally safer and tend to operate more
efficiently. For example, freeways only serve the mobility function and as a group have
the lowest crash rates and the highest level of operational efficiency.
Functional classification can be used to help prioritize roadway improvements.

The design features and level of access for specific roadways should be matched to the
intended function of individual roadways.

The appropriate balance point between the competing functions must be determined for
each roadway based on an analysis of specific operational, safety, design, and land features.

s
ay
sw
s
e
pr

Ex

No Thru Traffic
Low Speed

Mobility

10

Complete
Control

ls

ria

rte

ys
wa

igh

rA

no

nk

Tru

Mi

te
Sta ays
y
t
un hw
Co Hig
i
Ad

10

Access

Note: Percentage of
Roadway Mileage

s7

Pri

nci

ys
wa
e
e
Fr

pal

Arteri

als 5%

No Local Traffic
High Speed
MnDOT_A-12_5

Functional Classification System (1 of 2)

Source: FHWA Publication No. FHWA-RD-91-044 (Nov 1992)

Traffic Safety Fundamentals

Handbook2008

A-13

Typical Functionally
Classified Urban System
Highlights

Principal Arterial

Local Streets
Low volumes (less than 2K ADT)

Minor Arterial

Low speeds (30 MPH)

Moderate speeds (35 to 45 MPH)

Short trips (less than one mile)

Medium length trips (2 to 6 miles)

Two lanes

Three, four, or five lanes

Frequent driveways and intersections

Only major driveways

Unlimited access

Intersections at 1/4 mile spacing

75% system mileage / 15% VMT

10% system mileage / 25% VMT

Jurisdiction - Cities and Townships

Jurisdiction - Counties and Mn/DOT

Construction cost: $250K to

$500K/mile

Construction cost: $2.5M to

$7M / mile

Collector
Local Streets

MnDOT_A-13_1

Collectors
Lower volumes (1K to 8K ADT)

Minor Arterials
Moderate volumes (5K to 40K ADT)

Principal Arterials
High volumes (greater than 20K ADT)

ADT Average Daily Traffic

Lower speeds (30 or 35 MPH)

High speeds (greater than 45 MPH)

VMT Vehicle Miles Traveled

Shorter trips (1 to 2 miles)

Longer trips (more than 6 miles)

MPH - Miles Per Hour

Two or three lanes

4 or more lanes - access control

2K - 2,000

Frequent driveways

1M - 1,000,000

Intersections to 1/8th mile spacing

Intersections at 1/2 mile spacing and

Interchanges 1+ mile spacing

10% system mileage / 10% VMT

5% system mileage / 50% VMT

Jurisdiction - Cities and counties

Jurisdiction - Mn/DOT

Construction cost: $1M to $2M / mile

Construction cost: $10M to

$50M / mile

Functional Classification System (2 of 2)

Source: FHWA Publication No. FHWA-RD-91-044 (Nov 1992)

Traffic Safety Fundamentals

Handbook2008

A-14

Intersection Crash Rates (MN)

by Control Type and Family
Highlights

CRASH RATE (Crashes per MEV)

0.8
0.7

0.6

Crash frequency at intersections tends to be a function of exposure the

volume of traffic traveling through the intersection. As a result, the most
commonly used intersection crash statistic is the crash ratethe number of
crashes per million entering vehicles (MEV).

Crash frequency also tends to be a result of the type of traffic control at the
intersection. Contrary to the popularly held opinion that increasing the amount
of intersection control results in increased safety, the average crash rate at
signalized intersections (0.7 per MEV) is more than 150% higher than average
crash rate at stop signcontrolled intersections (0.3 per MEV). In addition, the
average severity rate and the average crash density is also greater for signalized
as opposed to stop sign controlled intersections.

It should be noted that approximately 40% of the Thru-STOP intersections had

no crashes in the 2004-2006 time period. At those intersections with crashes,
the average crash rate is approximately equal to the all STOP condition.

A wealth of research also supports the conclusion that traffic signals are only
rarely safety devices. Most Before vs. After studies of traffic signal installations
document increases in the number and rate of crashes, a change in the
distribution of the type of crashes, and a modest decrease in the fraction of
fatal crashes.

As a result of crash characteristics associated with signalized intersections,

installing traffic signals is NOT one of Minnesotas high priority safety strategies.

There is also data to support a conclusion that some type of left turn phasing
(either exclusive or exclusive/permitted), addressing clearance intervals and
providing coordination helps to minimize the number of crashes at signalized
intersections.

0.8

MEV = million entering veh.

> 15000 MEV (3) < 45 mph
< 15000 MEV (4) > 45 mph

(1)
(2)

0.6

0.7

0.7

0.6

0.5
0.4
0.3

0.3

0.2
A-14_v2

0.1
0.0
Thru-STOP

All STOP

(6236)

(59)

Signalized
Low Vol.(2)
Low Speed(3)
(152)

Signalized
High Vol.(1)

Signalized
Low Vol.(2)

Low Speed(3) High Speed(4)

(264)
(58)

Control Type/Family (no. of intersections)

Note: Only for Trunk Highway Intersections
Intersection Crashes (1 of 2)
Source: 2004-2006 Minnesota TIS Crash Data

Traffic Safety Fundamentals

Handbook2008

Signalized
High Vol.(1)
High Speed(4)
(382)

A-15

Intersection Crash Severity (MN)

by Control Type and Family
100%

1.2%

0.4%

90%

0.1%

29.1%

35.8%

0.2%

0.2%
33.2%

29.1%

0.2%

36.5%

80%

Highlights

2.0

The distribution of intersection crash severity appears

to be a result of the type/degree of intersection
control methods. Based on a review of over 31,000
crashes at more than 7,100 intersections, All-Way
STOPcontrolled and low speed/volume signalized
intersections were found to have the highest
percentage of property damage only crashes (71%)
and the lowest percentage of injury crashes (29%).
Intersections with traffic signal controls had the lowest
percentage of fatal crashes (0.2%).

The data also suggests that (on average) the installation

of a traffic signal does not result in a reduction in crash
severity. The severity rate at signalized intersections
(1.1) is about 120% higher than at intersections with
Thru/STOP controls (0.5).

This data supports the theory that increasing the

amount of intersection controls does not necessarily
result in a higher level of intersection safety.

33.7%
1.5

Percent

60%

70.5%

63.0%

66.6%

70.8%

50%

63.3%
1.0

66.1%
1.1

1.2

1.0

40%

0.8

Rate

70%

0.8

30%
0.5

0.5

20%
10%

Thru-STOP

All STOP

(6236)

(59)

Signalized
Low Vol.(2)

Signalized
High Vol.(1)

Signalized
Low Vol.(2)

Signalized
High Vol.(1)

Low Speed(3)
(152)

Low Speed(3)
(264)

High Speed(4)
(58)

High Speed(4)
(382)

Control Type/Family (no. of intersections)

Note: Only for Trunk Highway Intersections

Fatal

PDO

Injury

Severity Rate

PDO = Property Damage Only

MEV = Million Entering Veh.
(1) > 15000 MEV (3) < 45 mph
(2) < 15000 MEV (4) > 45 mph

A-15

0%

Source: 2004-2006 Minnesota TIS Crash Data

Intersection Crashes (2 of 2)

Traffic Safety Fundamentals

Handbook2008

A-16

Intersection Crash Distribution

by Rural vs. Urban
1% Right-Turn
3% Left-Turn

Thru/STOP

17% Rear End

53% Other

2% Right-Turn
7% Left-Turn

34% Other

25% Right Angle

32% Rear End

26% Right Angle

Rural
52% Rear End

Urban
1% Right-Turn
7% Left-Turn

Signalized

16% Right Angle

52% Rear End

1% Right-Turn
7% Left-Turn

23% Other

24% Other

17% Right Angle

Other Sideswipe (Passing/Opposing), Runoff Road, HeadOn, and Other/Unknown Crashes.

Note: Rural Refers to a nonmunicipal area and cities with a population less than 5,000.

Highlights

The crash type distribution that can be expected at

an intersection is primarily a function of the type of
intersection control.
At stopcontrolled intersections, in both rural and urban
areas, the most common types of crashes are right angle
and rear end collisions.
At signalized intersections, the most common types of
crashes are rear end, right angle, and left turn collisions.

Traffic Safety Fundamentals

Handbook2008

Several Key Points:

Traffic signals appear to reduce but not eliminate right angle crashes.

Right turns present a very low risk of a crash (1% to 2% of intersection crashes).

Left turns present a very low risk of a crash (3% to 7% of intersection crashes).

Crossing conflicts present a very high risk of a crash (16% to 26% of intersection crashes).

Rear end conflicts present the highest risk of a crash (17% to 52% of intersection crashes).

A-17

Roadway Segment Crash and Fatality

Rates by Jurisdictional Class
Roadway Jurisdiction
Classification

Miles

Crashes

Fatalities

Crash
Rate*

Fatality Rate**

Interstate

914

9,689

43

0.8

0.3

Trunk Highway

10,956

22,583

196

1.1

1.0

CSAH /County Roads

44,997

22,768

185

1.6

1.3

City Streets

19,105

21,423

41

2.7

0.5

Other (Township, etc.)

59,387

2,282

29

1.9

2.4

State Total

135,359

78,745

494

1.4

0.9

* per million vehicle miles (MVM)

** per 100 million vehicle miles (100 MVM)

Source: Minnesota Motor Vehicle Crash Facts (2006)

Highlights

As a class, interstates had lower crash and fatality rates than conventional
roadways. This is likely due to three factors:
Interstates only serve a mobility function

Interstates tend to have a consistently high standard of design
Interstates have very strict control of access

ounty and township roads had moderately high crash rates and the
C
highest fatality rates.

f the conventional roadways, Trunk Highways had the lowest crash rate
O
and the second lowest fatality rate.

City streets had the highest crash rate and a low fatality rate.

rash rates and fatality rates by roadway jurisdiction (and for the state
C
as a whole) are interesting, however, there is a great deal of evidence to
suggest that crash rates are more a function of roadway design than who
owns the road.

Traffic Safety Fundamentals

Handbook2008

his distribution of crashes generally supports the idea that greater

T
numbers of crashes occur in urban areas and greater numbers of fatal
crashes occur in rural areas.

A-18

Roadway Segment Crash Rates of

Facility Type by Rural vs. Urban
Highlights

Crash Rate (Crashes per Million Vehicle Miles)

5.0
4.7

4.5

Average crash rates vary by location (Rural vs. Urban) and

type of facility.

Freeways have the lowest crash rates and are the safest
0.308 in
roadway system in the state.

Rural roadways have lower crash rates than similar urban

roads.

Urban conventional roadways-often minor arterials which

serve both a mobility and land access functionhave the
highest crash rates.

Fourlane undivided roadways have the highest crash rate

these facilities are usually found in commercial areas with
high turning volumes and with little or no management of
access. Over the years, this average has been lowered (from
a rate of 8.0 in 1990), due to Mn/DOTs efforts to convert the
worst segments to either three-lane, four-lane divided or fivelane roads. The addition of left turn lanes to segments of urban
conventional roadways typically reduces crashes by 25% to
40%.

The distribution of crash rates by facility type points to the

relationship between access density and safetyhighways
with low levels of access (freeways) have low crash rates and
highways with higher levels of access (conventional roads)
have comparatively higher crash rates.

Rural
Urban

4.0
3.7

3.5

3.3

3.0
2.8

2.5
2.3

2.0

2.0

1.5
1.2

1.0

1.1
0.9

0.9

0.8

0.6

0.5
0

2-Lane

3-Lane

4-Lane
Undivided
Conventional

4-Lane
Divided

5-Lane

4-Lane
Divided

Interstate

Expressway

Freeway

Note: Only for Trunk Highway Segments

Rural Refers to a nonmunicipal area and cities with a population less than 5,000.
Source: 2004-2006 Minnesota TIS Crash Data

Traffic Safety Fundamentals

Handbook2008

A-19

Roadway Segment Crash

Distribution by Rural vs. Urban
Highlights

Urban

9% Run-Off Road

12% Sideswipe

4% Head On

20% Other

There is a significant difference in the types of crashes

that occur on urban versus rural roads.

Urban crashes are predominately two vehicle (about

85%) and rural crashes are predominately single vehicle
(about 55%).

The most common types of urban crashes include:

34% Rear-End
21% Right Angle

Rural

8% Sideswipe
7% Head On

14% Right Angle

15% Rear-End

_A-1

DOT

Mn/

Note: Only for Trunk Highway Segments

Rural Refers to a nonmunicipal area and cities with a population less than 5,000.

Percentages are rounded.

Rear-End (34%)

Right Angle (21%)

The most common types of rural crashes include:

Run off the Road (31%)

Rear-End (15%)

Right Angle (14%)

Some types of crashes are more severe than others. Only

7% of all rural crashes involve head-on collisions, but
they account for 20% of the fatal crashes.

Deer hits are underreported because they rarely result

in injury to vehicle occupants. A conservative estimate
is that as many as 24% of rural crashes involve hitting a
deer. For more information about collisions involving a
deer, see www.deercrash.com

31% Run-off Road

25% Other

Source: 2004 - 2006 Minnesota TIS Crash Data

Traffic Safety Fundamentals

Handbook2008

A-20

Roadway Segment Crash Rates as

a Function of Facility Type and
Access Density (MN)
Highlights

Urban

Rural

Previous safety research going back 30 years indicated a potential relationship between access
density and crash rates. However, this research did not account for other factors that are known
to affect crash rates (rural vs. urban, design type of facility, etc.) and none of the data was from
Minnesota.

As a result, in 1998, Mn/DOT undertook a comprehensive review of the relationship between

access and safety on Minnesota s Trunk Highway System. This effort ended with the publication
of Research Report No. 1998-27, Statistical Relationship Between Vehicular Crashes and
Highway Access.

The key components of the research included:

Conducting a detailed analysis of a 766-mile sample of the states 12,000 mile Trunk
Highway System.
Documenting the density of access and the crash characteristics on over 430 segments of
roadway.
Conducting rigorous statistical tests in order to achieve a high degree of statistical reliability.
Dividing the roadway segments into 11 separate categories in order to account for the
primary factors that account for the crash rate variability.

The significant results include:

Documenting for the first time the actual access density (an average of
8 per mile in rural areas and 28 per mile in urban areas).
Observing a statistical relationship between access density and crash rates in 10 of 11
categories.
Identifying a statistically significant tendency (in 5 out of 6 categories with sufficient sample
size) for segments with higher access densities to have higher crash rates in both urban and
rural areas.

2-Lane Conventional
4-Lane Conventional
Expressway
MnDOT_A-20_2

Crash Rate

6.0

3.0

8
0.0

28
15

30

45

Access Density
Note: Rural Refers to a nonmunicipal area and cities

with a population less than 5,000.
Source: Mn/DOT Research Report 1998-27 Statistical Relationship between Vehicular Crashes and Highway Access

Traffic Safety Fundamentals

Handbook2008

A-21

Safety Improvement Process

B-1

Minnesotas Strategic Highway Safety Plan (SHSP)

B-9

Supplemental Analysis: More Detailed Record Review

B-2

Minnesotas Safety Emphasis Areas

B-10 Mn/DOTs High CrashCost Trunk Highway Intersections

B-3

Safety Emphasis AreasGreater Minnesota vs. Metro

B-11 Systematic Analysis State Highways

B-4

Comprehensive Safety Improvement Process

B-12 Implementation Guidance for State Highways

B-5

Why Have a Black Spot Identification Process?

B-13 Systematic AnalysisCounty Highways

B-6

Alternative Methods for Identifying Potentially

Hazardous Locations

B-14 Implementation Guidance for County Highways

B-7

Effect of Random Distribution of Crashes

B-8

Calculating Crash Rates

B-15 Safety Planning at the Local Level

Education - Enforcement - Engineering - EMS - Data Systems

Minnesotas Strategic
Highway Safety Plan (SHSP)
MINNESOTA
Strategic Highway Safety Plan

Highlights

Minnesota Strategic Highway Safety Plan (SHSP) is a data driven

document that addresses the following issues:
Comprehensive: Addressed Four Safety Es
Systematic: Considered all roads

Identifies a new safety performance measure: Fatal and life-changing

injury crashes

Documents a new safety goal: 400 or fewer fatalities by 2010

Identifies a need to focus safety investments on rural areas and on local

systems in order to achieve the goal

Identifies the Critical Emphasis Areas (CEAs) and Critical Strategies

Driver behavior based emphasis areas
Unbelted vehicle occupants
Alcohol related
Speeding related
Young driver involved
Infrastructure-based emphasis areas
Intersection
Single vehicle road departure
Head-on and sideswipe

Includes both Proactive & Reactive Elements

June 2007

http://www.dot.state.mn.us/trafficeng/safety/shsp/index.html
SUBMITTED BY

TB042007001WDC

Traffic Safety Fundamentals

Handbook2008

B-1

Minnesotas Safety
Emphasis Areas
Statewide Fatalities (2001-2005)
Total Vehicle Occupant Fatalities..................................................................................................................................................... 2,429
Total Nonvehicle Occupant Fatalities (i.e., Pedestrian, Bicyclist)......................................................................................................... 579
Total Fatalities.................................................................................................................................................................................. 3,008

Driver Behavior Based Emphasis Areas

Number

Percentage*

Rank

Unbelted (Based on Veh. Occ. Fatalities)

1,271

(52%)

Alcohol-Related

1,068

(36%)

Speeding-Related

850

(28%)

Involved Drivers Under 21

718

(24%)

Number

Percentage*

Rank

1,004

(33%)

Single Vehicle Run Off Road

965

(32%)

Head-On and Sideswipe

611

(20%)

Infrastructure-Based Emphasis Areas

Intersection

Source: Minnesota Strategic Highway Safety Plan

*Note: Crashes may have more than one factor - percentages total more than 100%
establishing goals for proactively deploying low cost treatments widely
across systems of roadways, and revising the Highway Safety Improvement
Program in order to direct more resources to those elements of the system
that are most at riskrural highways and local roads.

Highlights

Guidance provided by Federal Highway and AASHTO suggest that state

and local safety programs will be the most effective if their implementation
efforts are focused on mitigating the factors that cause the greatest number
of fatal crashes.

An analysis of Minnesotas crash data documented the factors causing fatal

crashes; the results support designating seven safety emphasis areas in two
basic categories: Driver Behavior and Infrastructure.

Mn/DOT has taken the lead in addressing the Infrastructure based

Emphasis Area by adopting a focus on lane departure crashes in rural areas,

The Minnesota Department of Public Safety has taken the lead in

addressing the Driver Behaviorbased emphasis areas, mostly through
education and enforcement programs such as Click It or Ticket, Safe &
Sober, HEAT (High Enforcement of Aggressive Traffic), Safe Communities,
and a comprehensive set of limitations (hours of operation, number of
unrelated passengers, etc. ) for the most at risk group in Minnesota
teenager drivers.

Minnesotas Safety Emphasis Areas (1 of 2)

Traffic Safety Fundamentals

Handbook2008

B-2

Safety Emphasis Areas

Greater Minnesota vs. Metro
Total Fatalities

Driver Behavior Based Emphasis Areas

AlcoholSpeedingYoung Driver
Unbelted
Related
Related
Involved

Infrastructure Based Emphasis Areas

Single Vehicle
Head-on and
Intersection
Run Off Road
Sideswipe

Statewide
3,008

1,271
(52%)

1,068
(36%)

850
(28%)

718
(24%)

965
(32%)

1,004
(33%)

611
(20%)

284
(26%)
460
(47%)
744
(36%)

262
(24%)
284
(29%)
546
(26%)

224
(21%)
263
(27%)
487
(24%)

282
(26%)
459
(47%)
741
(36%)

360
(33%)
298
(31%)
658
(32%)

295
(27%)
129
(13%)
424
(21%)

167
(36%)
157
(33%)
324
(34%)

145
(31%)
159
(33%)
304
(32%)

103
(22%)
128
(27%)
231
(24%)

108
(23%)
116
(24%)
224
(24%)

126
(27%)
221
(46%)
347
(37%)

112
(24%)
76
(16%)
188
(20%)

Greater Minnesota Districts (2001-2005 Fatalities)

State Trunk Highway
Local Roads
Greater Minnesota
Districts Total

1,089
(53%)
974
(47%)
2,063

476
(49%)
492
(63%)
968
(55%)

Metro District (2001-2005 Fatalities)

State Trunk Highway
Local Roads
Metro District Total

465
(49%)
480
(51%)
945

Source: Minnesota Strategic Highway Safety Plan

162
(45%)
141
(45%)
303
(45%)

Represents at least 3% greater than statewide average

Highlights

lmost 70% of the fatalities in Minnesota are in the 79 counties outside of the 8 county Minneapolis St. Paul Metropolitan Area.
A
Fatal crashes are split almost evenly between the state and local roadway systems which results in higher fatality rates on the local system.
In Urban areas, the primary factors associated with fatal crashes are intersections and speeding.
In Rural areas, the primary factors associated with fatal crashes are not using safety belts, alcohol, and road departure crashes.

Minnesotas Safety Emphasis Areas (2 of 2)

Traffic Safety Fundamentals

Handbook2008

B-3

Comprehensive Safety
Improvement Process
Highlights

Implementation Strategies

Analytical Techniques

Reactive

Black Spot
Analysis

+
Proactive

For the past 30 years, most safety programs have been focused on
identifying locations with a high frequency or rate of crashes Black
Spots and then reactively implementing safety improvement
strategies.

The result of making Black Spots the highest priority in the safety
program was to focus safety investments primarily on urban and
suburban signalized intersectionsthe locations with the highest
number of crashes. However, these Black Spot intersections were
found to account for fewer than 10% of fatal crashes.

A new, more systematic based analysis of Minnesotas crash data

combined with the adoption of a goal to reduce fatal crashes has led
to a more comprehensive approach to safety programminga focus
on Black Spots in urban areas where there are intersections with
high frequencies of crashes and a systems-based approach for rural
areas where the total number of severe crashes is high but the actual
number of crashes at any given location is very low.

Fatalities

System Wide
Analysis

Years

Comprehensive Safety Improvement Process

B-04_v1

Traffic Safety Fundamentals

Handbook2008

B-4

Why Have a Black Spot

Identification Process?
Highlights

Urban

Rural

Rural Refers to a nonmunicipal area and cities with a population less than 5,000

Project Development

Crashes are one measurable indicator of how well a system of roadways

and traffic control devices is functioning.
Understanding safety characteristics can assist in the prioritization and
development of roadway improvement projects by helping document
Purpose and Need.

Risk Management

Actively identifying potentially hazardous locations is better than being in

the mode of reacting to claims of potentially hazardous locations by the
public (or plaintiffs attorneys).
Knowledge (actual or constructive) of hazardous conditions is one of
the prerequisites for proving government agency negligence in tort cases
resulting from motor vehicle crashes.
All crash analysis performed as part of a safety improvement program is
not subject to discovery in tort lawsuits.

Data Systems

Traffic Safety Fundamentals

Handbook2008

Conducting periodic Black Spot reviews of your system supports project

development activities and are an integral part of a best practices
approach to risk management. Monitoring the safety of your system
is good practice and is the industry norm against which you will be
evaluated.

In order to be able to develop countermeasures to mitigate the effects of

crashes, agencies need a monitoring system to identify crash locations
and the key characteristics and contributing factors associated with the
crashes. MnCMAT provides virtually all of the data necessary to support
Black Spot analyses.

B-5

Alternative Methods for Identifying

Potentially Hazardous Locations

1
2
3

Highlights

Number of
Crashes annually
is greater than X
crashes per year.
Crash Rate is
greater than Y
crashes per million
vehicles annually.

Critical Rate is a
statistically adjusted
Crash Rate to
account for random
nature of crashes.

Traffic Safety Fundamentals

Handbook2008

There are three primary methods for identifying potentially hazardous locations.

The first method would involve setting an arbitrary threshold value of X crashes per year at any particular location. This is
the simplest approach with the least data requirements. However, the selection of the threshold value is subjective and this
methodology does not account for variations in traffic volume or roadway design/traffic control characteristics.
This method is better than nothing and would be most applicable in systems consisting of similar types of roads with only
small variations in traffic volumes.

The second method consists of computing crash rates and then comparing them to an arbitrarily selected threshold value
of Y crashes per unit of exposure (a crash rate).
Disadvantages:
Advantage:
Allows comparison of facilities with different traffic
Subjective selection of the threshold value.
volumes.
Requires more data (traffic volumes).

Does not account for known variation in crash rates

among different types of road designs.

Does not account for the random nature of crashes.
Conclusion:
Limited applicability, better than just using crash frequency.

The third method involves using a statistical quality control technique called Critical Crash Rate
Advantage:
Disadvantage:
Only identifies those locations as hazardous if they
Most data intensive methodology (volumes and
have a crash rate statistically significantly higher than
categorical averages).
at similar facilities.
Conclusion:
Of these three methods, critical crash rate is the most accurate, and statistically reliable method
for identifying hazardous locations.

B-6

Effect of Random
Distribution of Crashes
Highlights

5.0
Locations statistically significant
above average due to defect in the location

Crash Rate

4.0

3.0

Locations above average

due to random nature of crashes

Critical Rate

The Concept of Critical Crash Rate

The technique that uses the critical crash rate is considered to be the best for
identifying hazardous locations.

The critical crash rate accounts for the key variables that affect safety, including:
The design of the facility
The type of intersection control
The amount of exposure
The random nature of crashes

The concept suggests that any sample or category of intersections or roadway

segments can be divided into three basic parts:
Locations with a crash rate below the categorical average: These locations are
considered to be SAFE because of the low frequency of crashes and can be
eliminated from further review.
Locations with a crash rate above the categorical average, but below the
critical rate: These locations are considered to be SAFE because there is a very
high probability (90-95%) that the higher than average crash rate is due to the
random nature of crashes.
Locations with a crash rate above the critical rate: These locations are
considered to be UNSAFE and in need of further review because there is a
high probability (90-95%) that conditions at the site are contributing to the
higher crash rate.

The other advantage of using the critical crash rate is that it helps screen out 90%
of the locations that do not have a problem and focuses an agencys attention and
resources on the limited number of locations that do have a documented problem
(as opposed to a perceived problem).

Average

2.0

1.0

Low

High

Exposure/Volume

Traffic Safety Fundamentals

Handbook2008

B-7

Calculating Crash Rates

Intersection Rates:

(number of crashes) x ( 1 million )

Rate per MEV

(number of years) x ( ADT ) x ( 365 )

Segment Rates:

(number of crashes) x ( 1 million )

Rate per MVM

(segment length) x (number of years) x ( ADT ) x ( 365 )

Critical Rate:
Rc = Ra + K x (Ra/m)+0.5/m

Rc = Critical Crash Rate

for intersections: crashes per MEV
for segments: crashes per MVM
Ra = System Wide Average Crash Rate by Intersection
or Highway Type
m = Vehicle Exposure During Study Period
for intersections: years x ADT x (365/1 million)
for segments: length x years x ADT x (365/1 million)
k = Constant based on Level of Confidence
Level of Confidence

0.995

0.950

0.900

2.576

1.645

1.282

MEV Million Entering Vehicles

MVM Million Vehicle Miles
ADT Average Daily Traffic on each leg entering an intersection or the daily two-way volume on a segment of roadway

Highlights

The number of crashes at any location is usually a function of exposure. As the number of vehicles entering an intersection or the vehicle miles of travel along a roadway
segment increase, the number of crashes typically increase.

The use of crash rates (crash frequency per some measure of exposure) accounts for this variability and allows for comparing locations with similar designs but different volumes.

Intersection crash rates are expressed as the number of crashes per million entering vehicles.

Segment crash rates are expressed as the number of crashes per million vehicle miles (of travel)

The Critical Crash Rate is calculated by adjusting the systemwide categorical average based on the amount of exposure and desired statistical level of confidence.

The difference between the systemwide categorical average and the critical rate increases as the volume decreases.

When computing the critical crash rate, the term m (vehicle exposure) is the denominator in the equations used in the calculation of either the intersection or segment crash rate.

The same formulas can be used to calculate fatality or injury rates, or the rate at which a particular type of crash is occurring.

A good rule of thumb is to use three years of crash data when available. More data is almost always useful, but increases the concern about changed conditions. Using only one
or two years of data presents concerns about sample size and statistical reliability.

Traffic Safety Fundamentals

Handbook2008

B-8

Supplemental Analysis:
More Detailed Record Review
Actual

vs.

Expected

Highlights

After identifying hazardous locations, the next

step is to conduct supplemental analyses in
order to better understand the nature of the
problem and to help develop appropriate
mitigative strategies.

A more detailed understanding of the

contributing factors is necessary to develop
countermeasures because there is currently
no expert system in place that allows mapping
from a high crash rate to the base safety
solution. Traffic engineers need to know more
about the particular problems at specific
locations because our Tool Kit is far less
developed than other areas of roadway
engineering.

The supplemental analysis of crash data

involves comparing ACTUAL crash
characteristics to EXPECTED characteristics
and then evaluating for differences. These
differences document crash causation factors,
which help identify effective countermeasures.

It is important to remember that roads that are

similar in design, with similar volumes will
operate in a similar manner and will probably
have similar crash characteristics.

Crash Rate
Severity
Type of Crash
Day/Night
Road Surface Condition
Driver Age
Driver Familiarity
Alcohol Involvement
Roadway Geometry
Access Density

Traffic Safety Fundamentals

Handbook2008

B-09_v2

Traffic Control Devices

B-9

Mn/DOTs High CrashCost

Trunk Highway Intersections
Highlights

Mn/DOT uses a number of techniques to identify potentially hazardous

locations, including critical crash rate, crash frequency, crash severity,
and crash cost.

Mn/DOT publishes a Top 200 list of high crash intersections along the
states 12,000 mile trunk highway system on an annual basis.

The list ranks intersections by crash cost, frequency, severity, and rate.

Intersections on the list generally have the following characteristics:

Crash frequencies between 1 and 63 per year.
Crash rates between 0.2 and 5.7 crashes per million entering vehicles.
Crash costs between $0.26 million and $1.2 million per year.

Listed intersections are overwhelmingly signalized (70%) and in

urban areas (69%).

In general, this approach does NOT adequately identify intersections

with safety deficiencies in rural areas.

This approach also does not necessarily identify locations with fatal
crashes (fewer than 10% of fatal crashes in Minnesota occurred at
intersections in the Top 200 list).

he key point is that a black spot analysis should continue to be a

T
necessary part of a comprehensive safety program, but a systematic
evaluation should also be performed.

Top 200 Intersections

Source: 2004 2006 Minnesota TIS Crash Data

Traffic Safety Fundamentals

Handbook2008

Trunk Highway High CrashCost Intersections

January 1, 2004 - December 31, 2006

B-10

Systematic Analysis
State Highways

Crash Summary by Facility Types Greater Minnesota Districts

2-Lane
2-Lane

Urban

Rural

Facility Type
Freeway
4-Lane Expressway
4-Lane Undivided
4-Lane Divided Conventional (Non expressway)
ADT < 1,500
1,500 < ADT < 5,000
5,000 < ADT < 8,000
ADT > 8,000
Sub Total
Freeway
4-Lane Expressway
4-Lane Undivided
4-Lane Divided Conventional (Non expressway)
Three-Lane
Five-Lane
ADT < 1,500
1,500 < ADT < 5,000
5,000 < ADT < 8,000
ADT > 8,000
Sub Total

Miles
702
712
27
123
3,774
3,916
583
198
10,034
21
41
43
66
30
12
81
238
111
75
718

Crashes
Serious
Fatal
Injury
54
77
49
94
0
4
11
24
48
74
110
185
45
52
24
35
341
545
2
7
4
19
1
20
8
45
0
10
2
4
1
4
0
22
10
19
5
19
33
169

Crash
Rate
0.6
0.8
0.9
1.2
0.8
0.7
0.9
0.9
1.4
2.4
3.9
3.3
2.8
2.8
1.9
2.1
2.0
2.6

Severity
Rate
Fatal Rate
0.8
0.6
1.2
0.8
1.4
0
1.9
1.2
1.4
1.9
1.2
1.4
1.4
1.7
1.4
1.5
1.9
3.5
5.6
5.1
3.8
3.9
3.0
3.0
2.8
3.7

0.3
0.9
0.3
1.2
0.0
1.6
1.8
0.0
1.9
0.8

Crash
Density
3.7
3.5
2.5
4.4
0.3
0.7
2.0
3.5

Priority

Historically, the absence of Black Spots in a system of roads was

interpreted to mean that there were no safety deficiencies and that there
were no opportunities to effectively make investments to reduce crashes.

However, a new interpretation of the crash data by the Federal Highway

Adminitration (FHWA) and an increasing number of state departments
of transportation suggests that neither of these assumptions is correct.

A review of Minnesotas crash data, conducted as part of the Strategic

Highway Safety Plan, provides several insights in support of a
systematic approach for addressing safety deficiencies.

On the states highway system, the facility types that present the greatest
opportunity to reduce fatal crashes (based on the total number of fatal
crashes) are rural two-lane roads (50%) and freeways (22%). However,
until recently there have been few projects on these facilities because
the process of filtering the data failed to identify any Black Spots.

Further analysis of these priority facilities shows that neither the overall
crash rate nor the fatality rate are at all unusual, but the pool of fatal
crashes susceptible to correction is still large and represents the greatest
opportunity for reduction: addressing road departure crashes on rural
twolane roads and cross-median crashes on freeways.

The final point in support of a systematic approach to address safety

in rural areas is the very low density of crashes along rural two-lane
highways 61% of fatal crashes occur on the 87% of the system that
averages less than one crash per mile per year.

Note: Crash rate is crashes per million vehicle miles; fatality rate is fatal
crashes per 100 million vehicle miles

21.3
12.6
16.9
17.6
10.1
13.7
0.7
2.4
4.6
10.5

Crash Summary by Facility Types Metro District

2-Lane
2-Lane

Urban

Rural

Facility Type
Freeway
4-Lane Expressway
4-Lane Undivided
4-Lane Divided Conventional (Non expressway)
ADT < 1,500
1,500 < ADT < 5,000
5,000 < ADT < 8,000
ADT > 8,000
Sub Total
Freeway
4-Lane Expressway
4-Lane Undivided
4-Lane Divided Conventional (Non expressway)
Three-Lane
Five-Lane
ADT < 1,500
1,500 < ADT < 5,000
5,000 < ADT < 8,000
ADT > 8,000
Sub Total
Source: Mn/DOT SHSP Crash Records, 2004-2005

Traffic Safety Fundamentals

Handbook2008

Miles
122
111
0
1
13
89
98
137
571
267
124
20
21
9
2
1
9
26
54
533

Crashes
Serious
Fatal
Injury
22
24
17
65
0
0
0
0
0
2
5
8
8
18
17
33
69
150
43
128
17
81
2
25
3
19
0
2
0
3
0
0
0
0
2
2
6
20
73
280

Crash
Rate
0.6
1.0
2.5
1.3
0.0
1.0
1.2
1.3
1.2
1.9
5.8
5.0
3.1
5.6
4.0
2.8
2.3
3.0

Severity
Rate
Fatal Rate
0.9
0.5
1.5
0.7
3.1
0.0
2.0
0.0
0.0
0.0
1.5
2.0
2.0
1.8
2.0
1.2
1.6
2.7
7.8
6.8
4.3
8.8
6.3
3.9
3.3
4.2

0.2
0.5
0.7
0.9
0.0
0.0
0.0
0.0
1.6
1.1

Crash
Density
11.1
10.3
14.8
9.2
0.5
1.3
2.7
6.9
41.7
23.9
41.3
38.6
16.8
52.4
2.1
3.7
5.5
15.6

Highlights

Priority

B-11

Implementation Guidance
for State Highways
Reactive

Proactive

Goal for Metro District

Moderate-Cost
High-Cost Improvements
Intersection
Improvements

50/50 GOAL
Corridor Management
and Technology
Improvements

Improve Traffic
Signal Operations

Employ ITS Technologies

Interchanges

Accel/Decel Lanes

Elec. Speed Enforcement

in School Zones

Indirect Turns

Access Management

Roundabouts

Goal for Greater Minnesota Districts

Low-Cost Intersection
Improvements

Road Departure
Improvements

Red Light Enforcement

Edge Treatments

Turn Lane Modifications

Enhanced Del. of Curves

Channelization

Safety Edge

Highlights

As part of the Strategic Highway

Safety Plan, Mn/DOT developed
implementation guidance for the districts.

The goal for districts in greater

Minnesota is to have a safety program
that is primarily focused on proactively
deploying (relatively) low-cost safety
strategies broadly across their systems of
rural two-lane roads and freeways.

The goal for the Metropolitan District is

to base their safety program primarily on
deploying generally higher cost safety
strategies at their Black Spot locations,
while reserving a small fraction of their
resources for widely deploying low-cost
new technologies or innovations across
their system.

After
Improve Sight Distance

Road Reconstruction
After

Before

Street Lights

Paved Shoulders
Rumble Strips/Stripes

Enhance Traffic
Signs and Markings

Cable Median Barrier

Curb Extensions

Upgrade Roadside Hardware

Road Safety Audit

After
Before

Before

Traffic Safety Fundamentals

Handbook2008

B-12

Systematic Analysis
County Highways
Freeborn County Road
Safety Audit Review
Analysis Model
10 Year Crash
Database in
County (7,034)

Additional Analysis to Support

Priorities of CEAs in Freeborn County
(20022006 Crash Data)
Freeborn County Crashes on
Conventional Roads (553)
35% State
Highway System

37%
Intersection
Related

Crash Types on
County System
(All Crashes)

63% Lane
Departure

Life Changing
(Ks + As) (114)
82% Lane
Departure

Freeborn County Emphasis Areas

s Rural Segments
Lane Departure Crashes
s Rural Intersections
Angle Crashes

An example of safety planning at

the local level is the work done by
Freeborn County.

The Countys crash data was analyzed

using the MnCMAT tool this analysis
identified Lane Departure crashes along
rural segments on the county system
and Angle crashes at rural intersections
as the highest safety priorities.

A review of crash data for the 2002

to 2006 timeframe found 65% of
the crashes on conventional roads
occurred on the county system.

The most relevant type of crash is lane

departure and 63% of these occurred
on the county system.

Lane departures accounted for 82% of

the severe crashes and 92% of these
occurred on the county system.

65% Freeborn
County System

All Crashes Coded

on or within 100'
of CSAH (1,872)

All County Road

Crashes (1,872)

Highlights

18%
Intersection
Related

Life Changing
Crashes on County
System (Fatal and
Severe Injuries)

Systematic Analysis of County Highways (1 of 2)

Source: Freeborn County Road Safety Audit Report, 2008

Traffic Safety Fundamentals

Handbook2008

B-13

Implementation Guidance
for County Highways
High Priority Locations on the Local System
Horizontal Curves:

Highlights

N
 o individual curves identified as Black Spots

The objective of the safety analysis conducted by

Freeborn County was to identify the primary causes
of their severe crashes and to conduct a mapping
exercise linking crash causation with a shortlist of
high priority safety strategies.

The review of county crash data found no Black

Spots on the county system, but did find a pool
of life-changing crashes (fatal+severe injury) that
would be susceptible to correction.

The safety analysis found that lane departure crashes

accounted for 87% of all life-changing crashes
and that 48% of these crashes occurred in curves
which make up only about 6% of the countys
highway system.

A field review of a sample of the countys system

found that about one-quarter of the curves (17 of
72) constituted a visual trap a horizontal curve
that followed a crest vertical curve or where there
was a township road on the extended tangent.

A shortlist of high priority strategies was developed

to address lane departure crashes and a method was
developed to assist in prioritizing horizontal curves
based on the number of crashes, curve radius,
presence of a visual trap, and proximity to other
high priority curves.

4
 8% of severe crashes in curves
1
 7 of 72 (24%) curves identified as visual traps

Lane Departure Crashes

Key Objectives:
Keep Vehicles in Their Lane
Key Strategies:
Improved curve
delineation
Improved lane markings

Key Objectives:
Improve Shoulders
Key Strategies:
Safety edge
Paved shoulders
Shoulder rumble strips

Rumble Strip
Key Objectives:
Improve Roadsides
Key Strategies:
C
 lear roadside of
fixed objects
B
 reakaway sign and
mailbox supports
Flatten slopes
Systematic Analysis of County Highways (2 of 2)

Without
Safety Edge

With
Safety Edge

Examples of implementations not

compliant with current standards

Source: Freeborn County Road Safety Audit Report, 2008

Traffic Safety Fundamentals

Handbook2008

B-14

Safety Planning at
the Local Level
Highlights

Traffic Safety Fundamentals

Handbook2008

Federal highway legislation requires all states to prepare Strategic Safety Plans, and all of
the states have complied.

However, both national and Minnesota crash data indicate that between 40 and 50%
of traffic fatalities occur on local roads this clearly indicates the need for local road
authorities to undertake their own strategic safety planning in order to support the
statewide effort.

Mn/DOT has supported safety planning at the local level by increasing levels of financial
assistance and technical support. The 2009-2010 Highway Safety Improvement Program
allocated almost $12M for 45 projects on the local system (including several projects that
involve the preparation of county strategic safety plans).

The single most important practice to support safety at the local level is for agencies to
dedicate a portion of their annual capital improvement program to implementing lowcost strategies on their system.

The preparation of a data driven Safety Plan will assist in identifying the primary
factors contributing to serious crashes, and this will assist in identifying the high
priority safety strategies. The overall objective is to develop a multi-year list of safety
improvement projects.

In addition to improvements to roadways, other local safety based practices could include:

Initiating/participating in a Safe Communities program

Initiating/participating in a Safe Routes to School program

Initiating a fatal crash review process

Participating in road safety audits

Support law enforcement initiatives to reduce speeding, improve seat belt

compliance and reducing drinking and driving.

B-15

Traffic Safety Tool BoxContents

C-1
C-2
C-3
C-4
C-5
C-6
C-7
C-8
C-9

Traffic Safety Tool BoxThen vs. Now

Traffic Safety Tool BoxThen vs. Now
Effectiveness of Safety Strategies
Roadside Safety Strategies
Edge Treatments
Horizontal Curves
Slope Design/Clear Recovery Areas
Upgrade Roadside Hardware
Effectiveness of Roadside Safety
Initiatives
C-10 Addressing Head-On Collisions
C-11 Intersection Safety Strategies
C-12 Conflict Points Traditional
Intersection Design

C-13 Conflict Points New

Intersection Design
C-14 Enhanced Signs and Markings
C-15 Intersection Sight Distance
C-16 Turn Lane Designs
C-17 Roundabouts and Indirect Turns
C-18 Traffic Signal Operations
C-19 Red Light Enforcement
C-20 Safety Effects of Street Lighting
at Rural Intersections
C-21 Flashing Beacons at Rural Intersections
C-22 Transverse Rumble Strips
at Rural Intersections

C-23 Pedestrian Safety Strategies

C-24 Pedestrian Crash Rates vs.
Crossing Features
C-25 Curb Extensions and Medians
C-26 Neighborhood Traffic Control Measures
C-27 Speed Zoning
C-28 Technology Applications
C-29 Work Zones
C-30 Crash Reduction Factors
C-31 Average Crash Costs
C-32 Crash Reduction Benefit/ Cost (B/C)
Ratio Worksheet
C-33 Typical Benefit/Cost Ratios for
Various Improvements

Traffic Safety Tool Box

Then vs. Now
Highlights

Then

THEN:

Only a few sources of information about the effectiveness of safety projects

were available, none were comprehensive and there were concerns

Now

about the statistical reliabilitySTOP

of the conclusions because of the analytical

techniques that were used. Most of the information available was based on
ONE WAY
observations of a limited
number of locations.

NOW:

Better and more comprehensive set of references are available:

NCHRP Series 500 Reports Implementation of AASHTOs Strategic

Highway Safety Plan

http://safety.transportation.org/guides.aspx

Report No. FHWA-SA-07-015 Desktop Reference for Crash

Reduction Factors

www.transportation.org/sites/safetymanagement/
docs/Desktop%20Reference%20Complete.pdf

Safety Analyst

www.safetyanalyst.org

Traffic Safety Tool Box (1 of 2)

Traffic Safety Fundamentals

Handbook2008

C-1

Traffic Safety Tool Box

Then vs. Now
Education

Enforcement

Older Drivers

Aggressive Driving

Distracted/Fatigued
Drivers

Unlicensed/
Suspended/Revoked
Drivers
License

Motorcycles

Alcohol

ME 4
VOLU

NC

IO
VE
VOLUME 15 NAT
RATI
OOPE

AL
ION
IVE
NAT PERAT
COO WAY
H
HIG ARCH
E
S
RE GRAM
O
PR

RT
50R0EPO
ORT

NAL

C
WAY
HIGH
ARCH
RESE
M
GRA
PRO

Head-On Crashes

Unsignalized
Intersections

he guides correspond to the 22 safety emphasis areas

T
outlined in AASHTOs Strategic Highway Safety Plan.

E ach guide includes a description of the problem and a list of

suggested strategies/countermeasures to address the problem.

he list of strategies in each guide was generated by an expert

T
panel that consisted of both academics and practitioners in
order to provide a balance and a focus on feasibility.

I n addition to describing each strategy, supplemental

information is provided, including the following;

Run-Off-Road
Crashes

Heavy Trucks

Pedestrians

Horizontal Curves

Signalized
Intersections

Utility Poles

Work Zones

00PORT 500
T 5RE
50
R0EPOR

REP

n of the
Implementatio Plan
Guidance efor
ay Safety
ategic Highw Guidance for Implementation of the
Strth
tion of
taHTO
AAS
the r Implemen
an
Plan
Pl
of
ty
n
fe
fo
Sa
AASHTO Strateg
for ic Highway Safety
tatio ance
ghway
emen Guafidety Plraan
e 15: A Guide y
tegic Hi
S
r Impl
Volum
nc for Addressing
hwaySHTO St
nce fo
erAgeGuide
ing Rural Em
ss
Guida ategic Hig AA
re
1:
e
dd
Volum
ing
g
A
s
sin for Enhancions
TO Str
AASH
e-Driving Collisions
dical Service
lis
ddres Guide

r Ae 6: A ns
d Col
uideVofolum ollisio-Off-Roa
4: A G Head-On C Run
lume

Vo

Me Aggressiv

he National Corporative Highway Research Program

T
(NCHRP) developed a series of guides to assist state and local
agencies reduce the number of severe crashes in a number of
targeted areas.

NATIONAL
COOPERATIVE
HIGHWAY
RESEARCH
PROGRAM

Trees in Hazardous
Locations

Unbelted
Occupants

L
NATIONA IVE
AT
COOPER
AY
HIGHW
CH
RESEAR
M
PROGRA

Highlights

P
RP
H
R
C
N
P
H
C
R
N
H
P
C
HRN
E
VOLUM

Engineering

Emergency
Services

Rural Emergency
Medical Services

Expected Effectiveness (crash reduction factors)

Implementation Costs

Challenges to Implementation

Organizational and Policy Issues

esignation of Each Strategy as either Tried, Experimental,

D
or Proven

http://safety.transportation.org/guides.aspx

Traffic Safety Tool Box (2 of 2)

Traffic Safety Fundamentals

Handbook2008

C-2

Effectiveness of
Safety Strategies
Highlights

Enforcement

Engineering

Graduated Drivers
Licensing
Safety Belt Enforcement
Campaigns
DWI Checkpoints
Street Lights at Rural
Intersections
Access Management
Roadside Safety
Initiatives
Pave/Widen Shoulders
Roundabouts
Exclusive Left Turn
Signal Phasing
Shoulder Rumble Strips
Improved Roadway
Alignment
Cable Median Barrier
Removing Unwarranted
Traffic Signals
Removing Trees in
Hazardous Locations
Pedestrian Crosswalks,
Sidewalks, and refuge
Islands
Left Turn Lanes on
Urban Arterial

Traffic Safety Fundamentals

Handbook2008

Engineering

Education

Tried

Rumble Strips
(on the approach
to intersections)
Neighborhood Traffic
Control
(Traffic Calming)
Overhead Red/Yellow
Flashers
Increased Levels of
Intersection Traffic
Control
Indirect Left Turn
Treatments
Restricting Turning
Maneuvers
Pedestrian Signals
Improve Traffic
Control Devices on
Minor Intersection
Approaches

Experimental

Engineering

Proven

Turn and Bypass Lanes

at Rural Intersections
Dynamic Warning
Devices at Horizontal
Curves
Static/ Dynamic Gap
Assistance Devices
Delineating Trees in
Hazardous Locations
Marked Pedestrian
Crosswalks at
Unsignalized
Intersections

Traffic Engineers have historically had a tool box of strategies that

could be deployed to address safety concerns. The results of recent safety
research studies suggest that the process for originally filling the tool box
appears to have been primarily based on anecdotal information.

The recent research efforts have subjected a number of safety measures

to a comprehensive package of comparative and before vs. after analyses
and rigorous statistical tests. The results of this research indicate that
some safety measures should be kept in the tool box, some removed,
some new measures added, and some continued to be studied.

The 22 volumes that make up the NCHRP Series 500 Reports

Implementation of AASHTOs Strategic Highway Safety Plan identify
over 600 possible safety strategies in categories including driver
behavior (speeding, safety belt usage and alcohol), infrastructure related
improvements (to reduce head-on, road departure and intersection
crashes) and providing emergency medical services.

These NCHRP Reports have designated each of the strategies as either

Proven (as a result of a rigorous statistical analysis), Tried (widely
deployed but no statistical proof of effectiveness) or Experimental (new
techniques or strategies and no statistical proof).

I t should be noted that virtually all of the strategies that have been
designated in the NCHRP Series 500 Reports as either Proven, Tried, or
Experimental are associated with engineering activities. This is due to
the lack of published research quantifying the crash reduction effects of
strategies dealing with Education, Enforcement, and Emergency Services.

C-3

Roadside Safety Strategies

Emphasis Area Objectives and Strategies
Objectives
15.1 AKeep
vehicles from
encroaching on the
roadside

Strategies

15.1 A1Install shoulder rumble strips

15.1 A2Install edgeline profile marking,
edgeline rumble strips, or modified shoulder
rumble strips on section with narrow or no
paved shoulders
15.1 A3Install midlane rumble strips
15.1 A4Provide enhanced shoulder or inlane delineation and marking for sharp curves
15.1 A5Provide improved highway
geometry for horizontal curves
15.1 A6Provide enhanced pavement
markings
15.1 A7Provide skid-resistant pavement
surfaces
15.1 A8Apply shoulder treatments
Eliminate shoulder drop-offs
Widen and/or pave shoulders

15.1 BMinimize

the likelihood of
crashing into an

object or overturning
if the vehicle travels
off the shoulder

15.1 B1Design safer slopes and ditches to

prevent rollovers
15.1 B2Remove/relocate objects in
hazardous locations
15.1 B3Delineate trees or utility poles with
retroreflective tape

15.1 C1Improve design of roadside

hardware (e.g., light poles, signs, bridge rails)
15.1 C2Improve design and application of
barrier and attenuation systems

15.1.CReduce the
severity of the crash

Roadside Safety Strategies (1 of 6)

Highlights

Single vehicle road departure crashes have been identified as being one of Minnesotas
Safety Emphasis Areas.

Single vehicle road departure crashes account for 32% of all fatal crashes in Minnesota
and as much as 47% of fatal crashes on local roads in rural areas.

The guidance in the NCHRP Service 500 Report Volume 6 suggests a three step
process for addressing road departure crashes:
1. Keep Vehicles on the Road
2. Provide Clear Recovery Areas
3. Install/Upgrade Highway Hardware

This three step priority is based on cost considerations, feasibility, and logic. The
strategies associated with keeping vehicles on the road are generally low cost, can easily
be implemented because additional right-of-way and detailed environmental analyses
are not required, and treating road edges directly
VOLUME 6
addresses the root cause of the problem vehicles
straying from the lane.

Providing clear recovery areas is considered to be

the second priority even though the strategies have
been proven effective, because of implantation
challenges costs are generally higher than for
edge treatments, and additional right-of-way may
be required as well as more detailed environmental
review.
Installing / upgrading highway hardware is the third
priority because it can be expensive to construct
and maintain, it can cause injuries when hit, and it
does not address the root cause of the problem.

NCHRP
REPORT 500

NATIONAL
COOPERATIV
E
HIGHWAY
RESEARCH
PROGRAM

Guidance for Imple

ment
AASHTO Strategic Highw ation of the
ay Safety Plan

Volume 6: A Guide
for Addressing
Run-Off-Road Collisio
ns

Source: NCHRP Report 500 Series (Volume 6)

Traffic Safety Fundamentals

Handbook2008

C-4

Edge Treatments
Highlights

Without
Safety Edge

Paved Shoulder and

Rumble Strip

With
Safety Edge

Rumble StripE

Typical edge treatments include shoulder/

edgeline rumble strips, enhanced
pavement markings, and eliminating
shoulder drop offs.

Implementation costs vary from no cost

(safety edge) to several thousand dollars
per mile for rumble strips/stripEs.

National safety studies have documented

crash reductions in the range of 20 to
50% for road departure crashes.

An unexpected benefit has been observed

on projects where edgelines have been
painted over the edgeline rumble strips
night time visibility in wet pavement
conditions was improved (the reflective
beads applied to the nearly vertical face
of the rumble strip remain above the film
of water on the pavement surface) and
the life of the pavement marking was
extended (snow plows cannot scrap away
the beads on the vertical faces).

Roadside Safety Strategies (2 of 6)

Traffic Safety Fundamentals

Handbook2008

C-5

Horizontal Curves
Highlights

4.0

Crash Rate, Crashes/MVM

85% Tangent Speed = 60MPH

A number of previously published research reports have identified

horizontal curves as at-risk elements of rural road systems, however, the
degree of risk was not quantified.

A recent report prepared by the Texas Transportation Institute (FHWA/

TX-07/0-5439-1) related actual crash rates on rural roads to the radius
of curvature. The results of this research indicates that the crash rate on
curves with radii greater then 2,500 feet is approximately equal to the
crash rate on tangent sections.

On curves with radii of 1,000 feet, the crash rate is twice the rate on
tangents and curves; curves with radii of 500 feet have crash rates eight
times higher than on tangents.

A number of safety studies that were focused on local, rural systems

in Minnesota have found road departure crashes are overrepresented
on horizontal curves 40 to 50% of the road departure crashes in the
selected counties occurred on curves, and curves made up less than
10% of the countys system.

The same studies also documented that over 60% of the horizontal
curves on the county system have radii less than 1,000 feet from a
system perspective, these curves are more at risk.

3.0

2.0

Fatal + Injury + PDO

Fatal + Injury
1.0

Bonneson et al. (5)

0.0

500

1000

MnDOT_C-06_2

Fitzpatrick et al. (6)

1500

2000

2500

Radius, ft
MVM Million Vehicle Miles
Source: Texas Transportation Institute (FHWA/TX-07/0-5439-1)
Roadside Safety Strategies (3 of 6)

Traffic Safety Fundamentals

Handbook2008

C-6

Clear Zone Distance

Through
Traveled Way Shoulder

Recoverable Slope
1:4 or Flatter Slope
(1:6 or Flatter Desirable)

Non- Recoverable Clear Runout

Slope
Area
1:6 or
Flatter Slope
Desirable

CZ = Clear Zone
ADT = Average Daily Traffic
Note: State-Aid projects use
the Mn/Dot State-Aid
Rural Design Standards.
Over 1,500 ADT; CZ = 30 FT
750-1,500 ADT; CZ = 20-25 FT
0-750 ADT;
CZ = 7-20 FT

Highlights

Providing clear recovery areas has been proven to reduce severe road departure crashes
by removing obstacles in hazardous locations and flattening shoulder slopes that cause
vehicles to roll over.

The recommended clear zone distance is a function of speed, slope, volume, and
horizontal curvature.

Generally, higher speeds, steeper fill slopes, higher volumes, and locations along the
outsides of horizontal curves require larger clear zones.

The concept of providing clear recovery areas is primarily intended for rural roadways.
However, the concept can be applied to suburban or urban roadways if road departure
crashes are a concern.

Source: Mn/DOT Road Design Manual

Traffic Safety Fundamentals

Handbook2008

Roadside Safety Strategies (4 of 6)

3:1

Slopes

Recovery Area
Clear Runout
Area Required

Example #1
6:1 Slope (Fill Slope)
60 MPH
5,000 ADT
Answer: CZ = 30 Feet
Example #2
6:1 Slope (Cut Slope)
60 MPH
750 ADT
Answer: CZ = 20 Feet

4:1
5:1
6:1
8:1
10:1
20:1

H
MP ed
50 esign Spe
D

PHed
60sM
pe
ign S
De

Traveled Way

Traveled Way

Obstacle

Slope

Obstacle

Fill Slopes

Flat

Slopes

Slope Design

40 MPH

Slope Design/Clear
Recovery Areas

20:1
10:1
8:1
6:1
5:1
4:1

Cut Slopes
e

Slop

Obstacle

Traveled Way

3:1
Over 6000 Design ADT

0' 10' 20' 30' 40' 50' 60' 70' 80' 90' 100'
1500-6000 Clear
Design ADTRecovery Area
0' 10' 20' 30' 40' 50' 60' 70' 80' 90'
750-1500 Design ADT
0'
10'
20'
30'
40'
50'
60'
70'
Under 750 Design ADT
50'
0'
10'
20'
30'
40'
Clear Zone Distance(CZ)

See Mn/DOT Road Design Manual

section 3.3.4 for a discussion on variable
slope determination

Note: Rural Refers to a nonmunicipal area and cities

with a population less than 5,000.

C-7

Upgrade Roadside
Hardware

Example implementations not compliant with current standards (NCHRP 350)

Highlights

Upgrading roadside hardware is a part of a comprehensive package of safety strategies aimed at reducing the severity of road departure crashes.

Typical treatments and their installation costs include the following:

Impact attenuator = $20,000

Guardrail terminal = $1,500

Guardrail transition = $1,000

W-Beam or Cable Guardrail = $75,000 - $150,000 per mile

Safety Benefits associated with using modern hardware involve reducing the severity of collisions with guardrail.

Roadside Safety Strategies (5 of 6)

Traffic Safety Fundamentals

Handbook2008

C-8

Effectiveness of Roadside
Safety Initiatives
40

TH 6
11.2
23

TH 38
Length (Miles)
Total Crashes (5 Years) +122%

11.2

PDO Crashes

25

12

Injury Crashes +117%

26

Fatal Crashes

1,100

Volume (VPD)

1,100

22.48

MVM

22.48

Crash Rates (Crashes/MVM) +130%

Engineering
1.5 Source: Mn/DOT District 1, TrafficSeverity

2.3

Source: Mn/DOT District 1, Traffic Engineering

+173%
4.1
Rate

1.3

Critical Crash Rates

1.3

10 (43%)

SVRD Crashes

37 (73%)

Hit Trees +1000%

30

8 (35%)

Passing Crashes

3 (6%)

Angle Crashes

Deer Hits

10 (43%)

Night

21 (41%)

Source: Mn/DOT District 1, Traffic Engineering

Traffic Safety Fundamentals

Handbook2008

Highlights

An estimate of the safety implications by evaluating two very

similar segments of two-lane rural trunk highways in northern
Minnesota: TH 6 and TH 38.

Both roads have the following similar characteristics:

Have virtually identical volumes
Serve similar functions (recreational and logging).
Traverse the Chippewa National Forest.
Have scenic qualities.

TH 6 has been reconstructed and TH 38 has not. (Note: This

segment of TH38 has recently been reconstructed but a Before vs.
After Study has not been completed)

The results are obvious. TH 38 has the following characteristics:

51

11

1.0

40

PDO
VPD
MVM
SVRD

More than twice as many crashes.

More than twice as many injuries.
A crash rate more than twice the average for two-lane rural
roads (and 30% greater than the critical rate).
Almost four times as many SVRD crashes (and more than
three the average for similar roads).
Ten times as many tree hits.
More than twice as many night time crashes.
Property Damage Only
Vehicles Per Day
Million Vehicle Miles
Single Vehicle Road Departure

Roadside Safety Strategies (6 of 6)

C-9

Addressing Head-On
Collisions
HeadOn Crashes on a TwoLane Rural Highway in Delaware
Before and After Use of Centerline Rumble Stripe

Highlights

HeadOn Crash Frequency

Severity of Crash

36 Months Before
6

Injury

14

12

Damage Only

19

VOLUME

Total

39

18

Crashes per Month

1.1

0.76

NCHRP
REPOR

T 500

NATIO
NAL
COOP
ER
HIGHW ATIVE
AY
RESEAR
CH
PROGRA
M

Guidance
AASHTO Stra for Implementation
of the
tegic Highw
ay Safety
Plan

Volume 4:

52

2004

2005

2006

2007

Cross-Median Fatalities

2003

2003

2004

2005

2006

270

30

240
25

210
180

20

150
120

270 10

30

240

90
60

210 5

25

180

20

150
120

10

Centerline rumble strips have been found to reduce head-on crashes along
two-lane roads data from 98 sites in 7 states (including Minnesota) indicated
significant reductions for injury crashes (15%) as well as for head-on and
opposing sideswipe injury crashes (25%).

Additional strategies for two-lane roads include conducting field surveys to

confirm that designated passing zones meet current guidelines for sight distance
and the use of thermoplastic markings where passing is not permitted.

The construction of Passing Lanes along two-lane roads has been found to
be a convenience for motorists (providing opportunities to pass slower moving
vehicles). However, there is no evidence that the passing lanes have reduced
head-on crashes.

A number of states have begun to address cross-median head-on crashes on

divided highways by installing cable median barriers. Reported reductions in
severe head-on crashes have ranged from 70 to 95%.

Mn/DOT has installed approximately 150 miles of cable barrier, with plans to
install an additional 80 miles. A preliminary analysis of Mn/DOTs first cable
median barrier installation (along I-94 in Maple Grove) found a 100% reduction
in fatalities and a 90% reduction in overall crash severity.

2007

I-44 Cross Median Fatalities

I-44 Cross Median Fatalities

Cross-Median Fatalities

2002

26

2002

Minnesota averages approximately 120 fatal head-on crashes per year, 90% are
passing related on two-lane facilities, slightly less than one-half are on the State
system, and about 75% are in rural areas.

26

20

50
40

20

Addressing head-on crashes is one of Minnesotas Critical Safety Emphasis areas.

50
40

30

1999

0
2000

2001

2002

2003

90
Source: AASHTO, Driving Down Lane Departure
Crashes, April 2008
60

30
0

2004

2005

2006

2007*

Guard Cable
Installation (miles)

52

40

Guard Cable
Installation (miles)

Fatalities

Fatalities

48

48

A Guide for
Addressing
Head-O

n Collision
s
Interstate Cross-Median
Fatalities

60

40

Source: NCHRP 500 Series (Volume 4)

Interstate Cross-Median Fatalities

Head-on crashes account for approximately 20% of the traffic fatalities in

Minnesota.

24 Months After

Fatal

60

0
1999

2000

2001

2002

Traffic Safety Fundamentals

Handbook2008

2003

2004

2005

2006

2007*

C-10

Intersection Safety Strategies

Relative Cost to
Implement and
Operate

Effectiveness

Typical Timeframe
for Implementation

A1-Implement intersection or driveway closures, relocations, and turning restrictions using

signing or by providing channelization.

Low to Moderate

Tried

Medium (1-2yrs.)

B1-Provide left-turn lanes at intersections; provide sufficient length to accommodate

deceleration and queuing; and use offset turn lanes to provide better visibility if needed.

Moderate to High

Proven

Medium (1-2yrs.)

B2-Provide bypass lanes on shoulders at T-intersections.

Low

Tried

Short (<1 yr.)

B3-Provide right-turn lanes at intersections; provide sufficient length to accommodate

deceleration and queuing; use offset turn lanes to provide better visibility if needed; and
provide right-turn acceleration lanes.

Moderate to High

Proven

Medium (1-2yrs.)

B4-Realign intersection approaches to reduce or eliminate intersection skew.

High

Proven

Medium (1-2yrs.)

C1-Improve visibility of intersections by providing enhanced signing. This may include

installing larger regulatory, warning, and guide signing and supplementary stop signs.

Low

Tried

Short (<1 yr.)

C2-Improve visibility of intersections by providing lighting (install or enhance) or red

flashing beacons mounted on stop signs.

Low to Moderate

Proven

Medium (1-2yrs.)

C3-Improve visibility of intersections by providing enhanced pavement markings, such

as adding or widening stop bar on minor-road approaches, supplementary messages (i.e.,
STOP AHEAD).

Low

Tried

Short (<1 yr.)

C4-Improve visibility of traffic signals using overhead mast arms and larger lenses.

Moderate

Tried

Short (<1 yr.)

C5- Deploy mainline dynamic flashing beacons to warn drivers of entering traffic.

Low

Experimental

Short (<1 yr.)

D-Improve sight distance at

intersections.

D1-Clear sight triangles approaches to intersections; in addition to eliminating objects in

the roadside, this may also include eliminating parking that restricts sight distance.

Low to Moderate

Tried

Short (<1 yr.)

E-Choose appropriate
intersection traffic control to
minimize crash frequency and
severity

E1-Provide all-way stop control at appropriate intersections.

Low

Proven

Short (<1 yr.)

E2-Provide roundabouts at appropriate intersections.

High

Proven

Long (>2 yrs.)

F-Improve driver compliance

with traffic control devices and
traffic laws at intersections

F1-Enhance enforcement of red-light running violations using automated enforcement

(cameras) or adding confirmation lights on the back of signals to assist traditional
enforcement methods.

Moderate

Proven/Tried

Medium (1-2yrs.)

G-Reduce frequency and

severity of intersection conflicts
through traffic signal control
and operational improvements.

G1-Employ multiphase signal operation, signal coordination, emergency vehicle

preemption optimize clearance intervals; implement dilemma zone protection; on high
speed roadways, install advance warning flashers to inform driver of need to stop; and
retime adjacent signals to create gaps at stop-controlled intersections.

Low to Moderate

Proven/Tried

Medium (1-2yrs.)

Objectives

Strategies

A-Improve access management

B-Reduce the frequency and
severity of intersection conflicts
through geometric design
improvements

C-Improve driver awareness of

intersections as viewed from the
intersection approach.

Source: Mn/DOT Strategic Highway Safety Plan

Addressing crashes at intersections is one

of Minnesotas Safety Emphasis Areas.

Intersection related crashes account for

more then 50% of all crashes and about
one-third of fatal crashes.

Approximately two-thirds of fatal

intersection crashes occur in Greater
Minnesota and slightly more than one-half
are on the local system.

STOP controlled intersections average

slightly less than 1 crash per year and
signalized intersections average almost 7
crashes per year.

The high priority safety strategies for

unsignalized intersections involve
managing access and conflicts, enhancing
signs and markings, improving intersection
sight distance and providing roundabouts.

The high priority strategies for signalized

intersections include reducing red
light violations and optimizing signal
operations.

VOLUME 12

NCHRP

AL
IVE
ION
NAT PERAT
O
AY
CO
HW
H
HIG EARC
RES GRAM
O
PR

P
NCHR

ME 5
VOLU

REP

REPORT 500

500
RT

Guidance for Implementation of the

AASHTO Strategic Highway Safety Plan

Intersections (1 of 8)

Highlights

e
n of th
entatio ty Plan
fe
plem
for Im ghway Sa
ance
Guid rategic Hi
ssing
TO St
ddre

A
ions
e for
Guid tion Collis
e 5: A
rsec
Volum ized Inte
al
n
g
si
Un

Volume 12: A Guide for

Reducing Collisions at
Signalized Intersections

NATIONAL
COOPERATIVE
HIGHWAY
RESEARCH
PROGRAM

On the state system, about 55% of intersection crashes occur at locations with STOP control. However,
there are 7 times as many STOP controlled as compared to signal controlled intersections.

The density of severe crashes (Fatals & A Injuries) is four times higher at signalized intersections than at
STOP controlled intersections.

AASH

Traffic Safety Fundamentals

Handbook2008

C-11

Conflict PointsTraditional
Intersection Design
Highlights

Full Access

Right In/Out
Access

A review of the safety research suggests that intersection crash rates

are related to the number of conflicts at the intersection.

Conflict points are locations in or on the approaches to an

intersection where vehicle paths merge, diverge, or cross.

The actual number of conflicts at an intersection is a function of the

number of approaching legs (T intersection have fewer conflicts
than 4-legged intersections) and the allowed vehicle movements
(intersections where left turns are prohibited/prevented have fewer
conflicts than intersections where all movements are allowed).

A preliminary review of intersection crash data indicates two key points:

Some vehicle movements are more hazardous than others. The

data indicates that minor street crossing movements and left
turns onto the major street are the most hazardous (possibly
because of the need to select a gap from two directions of
on-coming traffic). Left turns from the major street are less
hazardous than the minor street movements, and right turn
movements are the least hazardous.

Crash rates at restricted access intersections (3/4 design

and right in/out) are typically lower than at similar 4-legged
intersections. Prohibiting/preventing movements at an
intersection will likely reduce the crash rate.

3/4 Access
Typical Crash Rate

Crossing

Turning

Merge/
Diverge

Full Access

12

16

32

0.3 (1)

Full Access T

0.3 (2)

3/4 Access

10

0.2 (3)

Right In/Out Access

0.1

Total

(crashes per mil.

entering vehicles)

(3)

2004-2006 Minnesota TIS Crash Data

Estimated based on Publication FHWA-RD-91-048
(3)
Estimated based on a limited sample of Mn/DOT data
(1)
(2)

Intersections (2 of 8)

Traffic Safety Fundamentals

Handbook2008

C-12

Conflict PointsNew
Intersection Design
Full Access

CONTENTS

Indirect Left Turn Access

Roundabout
Access
Diverging
Merging
Crossing

(1)

Turning

Full Access

12

16

32

0.3 (1)

Roundabout

0.2 (2)

Indirect Left Turn

20

24

0.1 (3)

2004-2006 Minnesota TIS crash data

(2)

Merge/Diverge

Total

Typical Crash Rate (crashes

Crossing

Estimated based on a limited sample of Mn/DOT data

per mil. entering vehicles)

(3)

NCHRP 1530 Preliminary Draft

Highlights

Analysis of crash data proves that the most frequent type of severe intersection crash is a right angle vehicle maneuvers that involve crossing conflicts.

divided
In response
to this
data,
highway in
agencies
aredegree
beginning
to implement intersection designs that reduce or eliminate the at-risk crossing maneuvers by substituting
icts can be
into three
basic
categories,
which the
of severity
s, as follows: lower-risk turning, merging and diverging maneuvers. Two examples of these new designs include Roundabouts and Indirect Turn Treatments.

Roundabouts
have are
been
implemented
at a running
sufficient
number
of intersections in Minnesota and around the County, such that follow-up studies have documented a Proven
ueuing conflicts.
These conflicts
caused
by a vehicle
into
the back
a vehicle queue
on an approach.
These
types
of conflictsand
canseverity
occur of
at crashes.
the
effectiveness
of reducing
both
the frequency
More information regarding Roundabouts can be found at Roundabouts: An Informational Guide
ck of a through-movement
queue or where left-turning
vehicles are queued
(Report No. FHWA-RD-00-067
www.tfhrc.gov/safety/00-0675.pdf)
aiting for gaps. These conflicts are typically the least severe of all conflicts
The concept
of the
Indirect
has primarily
appliedand
to divided
roadways where there is sufficient room in the median to construct the channelization necessary to
cause the collisions
involve
mostTurns
protected
parts ofbeen
the vehicle
the
restrict crossing
maneuvers
to accommodate
U-turns. This design technique has been implemented at approximately a dozen intersections in Maryland and North
ative speed difference
between
vehiclesand
is less
than in other conflicts.
Carolina and as a result is considered Tried. Before/After studies at these locations have documented close to a 90% reduction in total crashes and a 100% reduction in
erge and diverge conflicts. These conflicts are caused by the joining or separatangle crashes. More information about Indirect Turns can be found in NCHRP 15-30: Median Intersection Design for Rural High Speed Divided Highways (currently in
g of two traffic streams. The most common types of crashes due to merge
draft formand
at rear-end
http://www.ctre.iastate.edu/educweb/nchrp%20final%20report/)
nflicts are sideswipes
crashes. Merge conflicts can be more seIntersections (2 of 8)

re than diverge conflicts due to the more likely possibility of collisions to the
de of the vehicle, which is typically less protected than the front and rear of the
hicle.
Traffic Safety Fundamentals

ossing
conflicts. These conflicts are caused by the intersection of two traffic
Handbook2008
eams. These are the most severe of all conflicts and the most likely to involve
uries or fatalities. Typical crash types are right-angle crashes and head-on crashes.

C-13

Enhanced Signs and Markings

Highlights

Add can delineators to Stop sign

36, reserve
48 for
intersections
with
documented
deficiency and
where there are
RR grade
crossings on the
CH approach
distance
between Stop
Ahead and Stop

Stop Bar,
12 to 24
wide,
8 to 12
back from
edgeline

Prioritized/Phasing
1. Stop bar
2. Stop sign
3. Junction sign
4. Stop Ahead Message

The most common type of crash at STOP

controlled intersections is a right angle crash.

Research performed in Minnesota (Reducing

Crashes at Controlled Rural Intersections Mn/
DOT No. 2003-15) found that approximately
60% of these angle crashes involved vehicles
on the minor road stopping and then pulling
out and 26% involved vehicles running
through the STOP sign.

This same study also found that increasing

the conspicuity of traffic control devices
by using bigger, brighter or additional signs
and markings (such as the STOP AHEAD
message and a STOP bar) are associated with
decreasing Run the STOP crashes.

A more recent Safety Evaluation of STOP

AHEAD Pavement Markings (FHWAHRT-08-043) documents the effects of
adding STOP AHEAD pavement markings.
The study looked at 175 sites in Arkansas,
Maryland and Minnesota. The study found
crash reductions in the range of 20 to 40%,
benefit/cost ratios greater than 2 to 1 and
concluded that this strategy has the potential
to reduce crashes at signalized intersections.

5. Stop Ahead Sign

distance
between Stop
Ahead and
Junction sign

Provide three devices indicating

up coming intersection

County Highway
(CH)

450 (min.) to
750 back, 1 size
larger than Stop
(up to 48)

Source: Mn/DOT Dist 3-13 County

RSA - CH2M HILL 2006
Intersections (3 of 8)

Traffic Safety Fundamentals

Handbook2008

C-14

Intersection Sight
Distance
Adequate Sight Distance

Highlights

MAJOR STREET

Clear Sight Lines

Intersection sight distance refers to the length of the gap along

the major roadway sufficient to allow a minor street vehicle to
either safely enter or cross the major traffic system.

A reasonable intersection sight distance allows for adequate

driver perception reaction time (2.5 seconds) and either
sufficient time to clear the major street, or to turn onto the
major street and accelerate to the operating speed without
causing approaching vehicles to reduce speed by more than
10 mph.

The actual length of the recommended intersection distance is

a function of the major street operating speed. However, the
size of the gap varies from 7 seconds at 30 mph to 10 seconds
at speeds of 60 mph and above.

When dealing with Mn/DOT's Trunk Highways, refer to

Section 5-2.02.02 of the Road Design Manual for additional
guidance regarding intersection sight distance.

It is important to note that intersection sight distance is

always greater than stopping sight distance, by as much
as 30 to 60%.

The ten second Rule of Thumb, 10 seconds of intersection

sight distance, is a good estimate regardless of conditions.

Removal of vegetation and onstreet parking are cost

effective safety improvements for intersections.

Intersection Sight Distance

10 ft.

STOP

MINOR
STREET

Speed
Intersection
Sight Distance

30

35

40

45

50

55

60

65

325 ft
7 sec.

400 ft
8 sec.

475 ft
8 sec.

550 ft
8 sec.

650 ft
9 sec.

725 ft
9 sec.

880 ft
10 sec

950 ft
10 sec

Inadequate Sight Distance

MAJOR STREET

View Obstructed by sign, vegetation,

utilities, and bus shelter.

Intersection Sight Distance

10 ft.

STOP

MINOR
STREET
Source: NCHRP Report 383 Intersection Sight Distance

Iowa Highway Safety Management System, and

AASHTO Green Book

Traffic Safety Fundamentals

Handbook2008

Intersections (4 of 8)

C-15

Turn Lane Designs

Highlights

Providing right and left turn lanes at intersections are included in Minnesotas
list of High Priority strategies.

However, there are locations where vehicles are stopped or decelerating in

the turn lane and can block the line of sight for other vehicles waiting at the
intersections. In these cases the use of Off-set left and right turn lanes will
improve the line of sight for vehicles waiting to complete their crossing or
turning maneuvers.

Off-set turn lanes are considered Tried (as opposed to Proven). A Before
vs. After Study of Off-set Left Turn lanes in North Carolina reported a 90%
reduction in Left Turn crashes. A similar study of Off-set Right Turn lanes in
Nebraska found a 70% reduction in near-side right angle crashes.

The Median Acceleration Lane (MAL) has been used at a number of locations
in Minnesota and is also considered Tried Before vs. After studies indicate a
75% reduction in same direction sideswipe crashes, a 35% reduction in farside right angle crashes and a 25% reduction involving left turn crashes from
the minor road.

OFF-SET
Left-Turn Lane

FIGURE 10 Green Book Exhibit 9-98; parallel and tapered offset left-turn lanes (3).

OFF-SET
Right-Turn Lane

FIGURE 85 PennDOT static gap assistance treatment application (89).

Median Acceleration Lane

Intersections (5 of 8)
F-8
Source: NCHRP 15-30 Preliminary Draft
Intersections (5 of 8)
Source: NCHRP
15-30 Preliminary
Draft
FIGURE
91 Offset right-turn
lane design concept illustration.

FIGURE 86 Expressway intersection with MALs.

F-77

Traffic Safety Fundamentals

Handbook2008

C-16

Roundabouts and Indirect Turns

Highlights

Minessota TH13 at Scott

County Highway 2
Source: Mn/DOT Metro
District Before: After Study

The most common and most severe type of crash at STOP controlled intersections is
a Right Angle which involves a vehicle on the minor road attempting to select a safe
gap along the major highway in order to cross.

A proven strategy to reduce gap selection related angle crashes involves redesigning
the intersection or median cross-over to eliminate crossing conflicts (which have the
highest probability of a crash) by substituting merging, diverging or turning conflicts
(which have a lower probability of a crash).

The primary examples of reduced conflict intersection designs include; Roundabouts,

J-Turns and special application for T intersections the Partial Interchange.

Roundabouts are considered to be Proven effective (there is virtually no possibility

of an angle crash) with statistically significant crash reductions 38% for all crashes,
76% for injury crashes and for serious injury and fatal crashes. Not withstanding the
superior safety performance, care must be taken when considering conversion to a
Roundabout implementation costs are in the range of $1,000,000 and all entering
legs are treated equally. The key question is do the traffic characteristics and function
classification support the degrading of mainline traffic operations.

The concept behind indirect-turns is that merge, diverge and turning conflicts result
in fewer and less severe crashes. An example of the indirect turn applied to a divided
roadway is the J-Turn. This application involves constructing a barrier in the median
cross-over and forcing minor street crossing traffic to instead make a right turn,
followed by a downstream U-Turn, followed by another right turn. J-Turns have been
Tried at about a dozen locations in Maryland and North Carolina implementation
costs are in the range of $500,000 to $750,000 and a preliminary crash analysis
found a 100% reduction in angle crashes and a 90% reduction in total crashes.

The partial interchange is an interesting concept for T intersections along divided

roadways the construction of one bridge on the near-side of the intersection
eliminates all crossing maneuvers. This concept is being considered for several
locations in Minnesota, but deployment has not been sufficiently wide spread to be
able to identify typical implementation costs or document crash reductions.

Indirect Turns

FIGURE 47 J-turn intersection conceptual schematic.

Source: NCHRP 15-30

Partial T-Interchange

FIGURE 48 Conflict point diagram for J-turn intersection.

Intersections (6 of 8)

Traffic Safety Fundamentals

Handbook2008

F-38

C-17

Traffic Signal Operations

Highlights

Installing traffic signals is NOT considered to be a High Priority Intersection Safety Strategy because of the results of studies done at both the national level and in
Minnesota. At most intersections, the installation of a traffic signal will increase the number of crashes, along with increasing crash and severity rates. Also, as a
category signalized intersections have a higher average crash density, crash rate and severity rate than the average for STOP controlled intersections.

However, if a traffic signal must be installed to address intersection delay and congestion, there are several suggested High Priority strategies to reduce frequency
and severity of intersection crashes. These include:

Use of multiphase signal operation combined with left turn lanes.

Provide dilemma zone protection and optimize clearance intervals

Provide a coordinated signal system along urban arterials

Use overhead indicationsone per through lane mounted at the center of

each lane

Use advance warning flashers to supplement static signs where a signal

may be unexpected.

Pedestrian indications including the use of count down timers.

Intersections (5 of 8)

Traffic Safety Fundamentals

Handbook2008

C-18

Red Light Enforcement

Highlights

Confirmation
Light In Florida

Signalized
16% Rear End
22% Other

16% Rear End

14% Left-Turn
22% Other

14% Left-Turn

48% Right Angle

Thru-Stop or Yield25%Controlled
Other
25% Other

60% Right Angle

60% Right Angle

5% Rear End

48% Right Angle

5% Rear End

10% Left-Turn

Other Sideswipe (Passing/Opposing), Runoff Road, Right Turn, and

Head-On Crashes

10% Left-Turn

The most common type of severe crash at signalized intersections is a Right

Angle. Even though signals are intended as a mitigation for angle crashes they
have proven to be only marginally effective. In the Minneapolis-Saint Paul
Metropolitan area, the annual number of severe angle crashes at signalized
intersections (160) exceeds the number at STOP controlled intersections (120),
even though the number of STOP controlled intersections exceeds the number of
signalized intersections by a factor of 4.

Crash analysis indicates that most angle crashes at signalized intersections are
caused by red light violations.

As a result, one of Minnesotas adopted High Priority Safety Strategies involves

enhancing the enforcement of red-light violations.

A number of states are using technology to supplement traditional enforcement of

red light violations. This involves the use of Red Light Camera Systems in states
with enabling legislation (Not Minnesota).

Studies of RLC systems (including Safety Evaluation of Red Light Cameras, FHWAHRT-05-048) have documented 40% reductions in red light violations, 25%
reductions in angle crashes and a 15% overall reduction in total intersection
crashes. The studies also noted a modest increase in rear end crashes, but these
tended to be less severe so the average value of crash reduction approached
$50,000 per site per year.

Florida is a state that does not allow RLC systems, so they developed a strategy
that uses confirmation lights mounted on the signal mast arms combined with a
partnership with local law enforcement. The confirmation light allows one officer
to safely observe and pursue red light violators (instead of one officer to observe
and an additional officer to pursue). Confirmation lights are inexpensive ($500
to $1,000 per mast arm) and a preliminary evaluation of installations in Florida
found a 50% decrease in violations and a 10% overall decrease in crashes.

For more information see www.stopredlightrunning.com

Intersections (6 of 8)

Traffic Safety Fundamentals

Handbook2008

C-19

Safety Effects of Street Lighting

at Rural Intersections
System-Wide Comparative Analysis
Intersections without
Intersections
Statistical
Street Lights
with Street Lights Reduction Significance

Item
Intersections

3236

259

Night Crashes

34%

26%

26%

Yes

Night Crash Rate

0.63

0.47

25%

Yes

Night Single Vehicle Crashes

23%

15%

34%

Yes

Night Single Vehicle Crash Rate

0.15

0.07

53%

Yes

Highlights

The installation of street lights is considered to be a Proven

effective strategy for reducing crashes.

Research has found that the installation of street lights at rural

intersections reduced:

Before vs. After Crash Analysis

Item

Statistical
Reduction Significance

Before

After

Intersections

12

12

Number of Night Crashes

47

28

40%

Yes

Night Crashes/Intersection/Year

1.31

0.78

40%

Total Crashes/Intersection/Year

2.44

2.08

15%

Night Crash Rate

6.06

3.61

40%

Yes

Total Crash Rate

2.63

2.24

15%

Yes

Severity Index

43%

32%

26%

Yes

Night Single Vehicle Crash Rate

4.0

2.84

29%

Yes

Night Multiple Vehicle Crash Rate

2.06

0.77

63%

Yes

Traffic Safety Fundamentals

Handbook2008

Night Crashes by 26% to 40%

Night Crash Rate by 25% to 40%

Night Single Vehicle Crashes by 29% to 53%

Night Multiple Vehicle Crashes by 63%

Night Crash Severity by 26%

A Benefit versus Cost analysis found that the crash reduction

benefits of street lighting at rural intersections outweigh costs
by a wide margin. The average B:C ratio was about 15:1.

The results of recent case study research suggests that the use
of street lighting is more effective at reducing night crashes
than either rumble strips or overhead flashers.

A survey of practice among Minnesota counties found typical

lighting installation costs along county facilities in the range
of $1,000 to $5,000 per intersection and annual operations
maintenance costs in the range of $100 to $600 per light.

C-20

Flashing Beacons at
Rural Intersections
STOP

Old

New

Y
R

STOP

Source: Warning Flashers at Rural Intersection, Minnesota Department of Transportation Final Report No. 1996-01. 1997

Highlights
A review of historic crash data indicated that STOP controlled rural intersections with overhead flashers had higher average
crash rates than comparable intersections without overhead warning flashers.

Anecdotal information that surfaced during the investigation of several fatal crashes indicated that some drivers were
mistaking Yellow/Red warning flashers for Red/Red flashers that would indicate an All-Way STOP condition.

In order to address the issue of effectiveness, Mn/DOT commissioned a study by the University of Minnesotas Human Factors
Research Lab. The study resulted in the following conclusion:

About one-half of drivers surveyed understood the warning intended by the flasher, but most did not adjust their behavior.

About 45% of the drivers misunderstood the intended message and thought it indicated an All-Way STOP condition.

The change in crash frequency at a sample of intersections was NOT statistically significant.

In response to this research, Mn/DOT has begun removing

overhead flashers.

Where there is evidence that additional intersection warning is necessary, options includeuse of red flashers on STOP signs
or advance warning flashers on STOP AHEAD signs (but there are no studies documenting effectiveness).

Traffic Safety Fundamentals

Handbook2008

STOP

STOP

C-21

Transverse Rumble Strips

at Rural Intersections
Highlights

Number of Crashes (3-Year Period)

Number of Accidents

70
60

Before Installation of Rumble Strips

50

After Installation of Rumble Strips

40

The use of transverse rumble strips to address safety issues at rural intersections
has been part of the traffic engineers tool box for many years. However, there
are no definitive studies documenting their actual effectiveness.

Mn/DOT took the opportunity to perform a thorough study of transverse rumble

strips as part of preparing their defense in a lawsuit alleging negligence on the
states part for not having rumble strips at a particular intersection. The study
resulted in the following conclusions:

30
20
10

59

66

21

27

21

18

Total

Right Angle

Percentage

12%

A Before versus After analysis of 25 rural intersections in Minnesota found

that total intersection crashes and right angle crashes actually increased after
installing rumble strips. The number of fatal plus injury crashes declined
slightly; however, none of the changes was statistically significant.

Recent work by the University of Minnesotas Human Factors Research Lab

found that rumble strips had a minor effect on driver behavior relative to speed
reduction and breaking patterns. However, there was no evidence of crash
reduction.

For more information, see Mn/DOTs Transportation Synthesis Report, TRS 0701.
www.lrrb.org/trs0701.pdf

Strategies that been proven effective at improving safety at improving safety at

rural Thru/STOP intersections include enhanced signs, markings (C-14) and street
lights (C-20).

29%

Right Angle Crashes

-14%

Total Crashes

Based on a search of previous research, no one has ever documented

statistically significant crash reductions attributed to the installation of
transverse rumble strips on the approach to stop controlled intersections.

Fatal & Personal

Injury

Before vs. After Change

30%
25%
20%
15%
10%
5%
0%
-5%
-10%
-15%
-20%

Fatal & Personal

Injury Crashes

Effectiveness of Rumble Strips at Rural Intersections

Source: Mn/DOTs Transportation Synthesis Report, TRS 0701, August 2007

Traffic Safety Fundamentals

Handbook2008

C-22

Pedestrian Safety
Strategies
Highlights

Emphasis Area Objectives and Strategies

Objectives

Strategies

9.1 A Reduce Vehicle Speed

9.1 A1 Implement Road Narrowing Measures

9.1 A2 Install Traffic CalmingRoad Sections
9.1 A3 Install Traffic CalmingIntersections
9.1 A4 Provide School Route Improvements

9.1 B Improve Sight

Distance and/or Visibility
between Motor Vehicles and
Pedestrians

9.1 B1 Implement Lighting/Crosswalk Illumination Measures

9.1 B2 Provide Crosswalk Enhancements
9.1 B3 Improve Reflectorization/Conspicuousness of Pedestrians

9.1 C Reduce Pedestrian

Exposure to Vehicular Traffic

9.1 C1 Provide Vehicle Restriction/Diversion Measures

9.1 C2 Construct Pedestrian Refuge Islands and Raised Medians
9.1 C3 Install or Upgrade Traffic and Pedestrian Signals
9.1 C4 Provide Sidewalks/Walkways and Curb Ramps
9.1 C5 Install Overpass/Underpass

9.1 D Improve Pedestrian and

Motorist Safety Awareness and
Behavior
Source: NCHRP Series 500 (Volume 10)

Fatal crashes involving pedestrians are one of AASHTOs

Safety Emphasis Areas. In the U.S., there are about 5,000
pedestrians killed each year, which represents about 11%
of all traffic fatalities.

Minnesota averages about 45 pedestrian fatalities

annually (about 8% of total traffic fatalities) and our
involvement rate (0.4 pedestrian fatalities per 100,000
population) ranks 47th only Rhode Island, New
Hampshire, and Idaho have a lower rate.

Fatal pedestrian crashes most often occur in urban areas

(17%), away from intersections (78%), during good
weather (64%). Over two-thirds of the pedestrians killed
are male.

The most common pedestrian activities associated

with fatal crashes are walking/working in the road and
crossing the roadway.

The pedestrian was coded for a contributing factor

(running into the road 15%, Failure to yield 12%, and
Alcohol 10%) in 66% of the crashes vs. 55% for the
motorist (Hit & Run 16% and Failure to yield 15%).

The safety strategies in NCHRP Series 500, Vol. 10 are

focused on reducing vehicle speeds, improving sight
lines, reducing exposure to traffic, plus education and
enforcement activities.

9.1 D1 Provide Education, Outreach, and Training

9.1 D2 Implement Enforcement Campaigns
VOLU
M

NCHR
E 10

REP
ORT

500

NATI
CO ONAL
O
HIG PERATI
H
VE
RES WAY
PRO EARCH
GRA
M

Guid
AASH ance for
TO St
Implem
ra

tegic
en
Volum
Highw tation of
th
ay Sa
e
fety Pl e
Collis 10: A Guid
an
ions
Involv e for Red
ucing
ing P
edes
trians

Pedestrian Safety Strategies (1 of 3)

Traffic Safety Fundamentals

Handbook2008

C-23

Pedestrian Crash Rates vs.

Crossing Features
Pedestrian Crash Rate

(Pedestrian Crashes per Million Crossings)

1.6
1.4

Sig. = Significant Difference

Sig.

Highlights

Crosswalk Type

N.S. = No Significant Difference

M = Marked

Three of the more common strategies intended to address pedestrian crashes include
reducing vehicle speeds, providing a marked crosswalk, and installing a traffic signal.

The research is abundantly clearmerely changing the posted speed limit has never
reduced vehicle speeds, painting cross-walks at unsignalized intersections is actually
associated with higher frequencies of pedestrian crashes, and installing a traffic signal
has never been proven effective at reducing pedestrian crashes.

Reducing vehicle speeds is associated with reducing the severity of a pedestrian crash,
but actually reducing speeds requires changing driver behavior and that requires
changing the roadway environment. Strategies that have demonstrated an effect on
driver behavior include vertical elements (speed bumps and speed tables), narrowing
the roadway (converting from a rural to an urban section) and extraordinary levels of
enforcement).

A cross-sectional study of 2,000 intersections in 30 cities across the U.S. found that
marked cross-walks at unsignalized intersections are NOT safety devices. The pedestrian
crash rate was higher at the marked cross-walks and this effect is greatest for multi-lane
arterials with volumes over 15,000 vehicles per day.

A Before versus After study at over 500 intersections in San Diego and Los Angeles found
a 70% reduction in pedestrian crashes following the removal of marked cross-walks at
uncontrolled intersections.

Traffic signals have not proven to be effective at reducing pedestrian crashes the highest
pedestrian crash frequency locations in most urban areas are signalized intersections.

Observations of pedestrian behavior at traffic signals suggests that there is a low level of
understanding of the meaning of the pedestrian indications and a high level of pedestrian
violationsvery few push the call button and fewer yet wait for the walk indication.

U = Unmarked

1.2

.10

Sig.

.08
Sig.
0.6

0.4
N.S.
0.2
0

N.S.

N.S.

0.12 0.12
M

No Median
All ADTs
2 Lanes
(914 Sites)

0.17 0.25
M

No Raised
Median
12,000 ADT
3-8 Lanes
(260 Sites)

0.63 0.15
M

No Raised
Median
12,000-15,000 ADT
3-8 Lanes
(149 Sites)

1.37 0.28
M

No Raised
Median
>15,000 ADT
3-8 Lanes
(417 Sites)

0.17 0
M

Raised Median
15,000 ADT
3-8 Lanes
(87 Sites)

0.74 0.17
M

Raised Median
>15,000 ADT
3-8 Lanes
(173 Sites)

Type of Crossing
Source: Charles V. Zegeer, et al., Safety Effects Of Marked Vs. Unmarked Crosswalks At Uncontrolled
Locations: Executive Summary And Recommended Guidelines, 1996-2001,
http://www.walkinginfo.org/pdf/r&d/crosswalk_021302.pdf

Pedestrian Safety Strategies (2 of 3)

Traffic Safety Fundamentals

Handbook2008

C-24

Curb Extensions
and Medians
Highlights

Median Refuge
Near Intersection

Pedestrian strategies that have proven to be

effective include the following:

Overpass (in order to be effective,

crossing the roadway at-grade must be
physically prevented)

Street Lighting

Refuge/Median Islands Reduces

vehicle speeds at pedestrian crossing
locations or intersections.

Curb Extensions Reduces potential

vehicle conflicts by reducing pedestrian
crossing distance and time. Also,
improves lines of sight.

Sidewalks

Curb Extensions and

Sidewalks

Pedestrian Safety Strategies (3 of 3)

Traffic Safety Fundamentals

Handbook2008

C-25

Neighborhood Traffic
Control Measures
Highlights

Neighborhood traffic control (traffic calming) usually involves

applying design techniques and devices on local streets in order to
modify driver behavior and traffic characteristics.

The application of these devices are usually limited to residential

streets, have been infrequently used on residential collectors and
should not be considered on arterials due to the presence of transit
vehicles, trucks and emergency responders.

Typical techniques involve the use of signs, markings, road narrowing

or diverters, vertical elements and the use of technology to increase
the enforcement presence.

A few studies of the effectiveness of these devices have been

conducted the general conclusions are:

Source: ITE Traffic Calming Seminar

Source: ITE, Traffic Calming State of the Practice

Speed humps/bumps are moderately effective at lowering speeds

in the range of 3 to 7 mph (in the immediate vicinity of the
device).

Adding STOP signs lowers speeds by about 2 mph, in the vicinity

of the STOP sign, but also reduces compliance a greater
number of drivers completely disregard the sign than come to
a complete stop. In addition, speeds in the segments between
STOP signs have been observed to increas drivers attempting to
make up for lost time.

Changing speed limit signs has never changed driver behavior.

Enforcement does change driver behavior only when present.

https://www.ite.org/traffic/tcstate.htm

Traffic Safety Fundamentals

Handbook2008

C-26

Speed Zoning

Study
Location

Freeways

(Crashes
per Million
(Crashes per Million
Vehicle
Miles)Vehicle Miles)

-40
8

10
6
8
4

-30

6.96

-20

-10

SPEED
LIMIT

SPEED
LIMIT

SPEED
LIMIT

Anoka
CSAH 1

SPEED
LIMIT

SPEED
LIMIT

Anoka
CSAH 24

SPEED
LIMIT

SPEED
LIMIT

Anoka
CSAH 51

SPEED
LIMIT

SPEED
LIMIT

Hennepin
CSAH 4

SPEED
LIMIT

SPEED
LIMIT

10

20

30

SPEED
LIMIT

SPEED
SPEED
LIMIT

SPEED
SPEED
LIMIT

SPEED
LIMIT

T.H. 65

40

Noble Ave

62nd Ave N

6.96 3.94
3.94

4.30

4.30

Miss. St

3.37

90 Segments
59 Miles
3750 Crashes

18 Segments
8 Miles
496 Crashes

20 Segments
24 Miles
1470 Crashes

23 Segments
12 Miles
403 Crashes

30

35

40

45

2
0

SPEED
LIMIT

T.H. 65

Deviation from Average Speed, mi/h

6
2
4
0

After

Freeways

100
1000

100
-40 -30 -20 -10 0 10 20 30 40
Deviation
from Average Speed, mi/h
1968
Source: Solomon, 1964, and Cirillo,

10

10000
1000

Before

Nighttime (rural)
Daytime (rural)

3.37

40

30

50

40
40

45
30

45

40

45

50

40

30
35

SPEED
LIMIT

30

35
30

Sign
Change
+/- MPH

85%
Before
After

-10

34
34

-10

44
45

+1

-5

48
50

+2

+15

49
50

+1

+5

45
46

+1

-10

52
51

-1

+5

37
40

+3

-5

37
37

39
40

+1

185 Segments
128 Miles
SPEED
SPEED
7028 Crashes
LIMIT
35 Average+5
Statewide
= 4.0

2.38 2.32

30

50

35

40

45

50

10 Segments
12 Miles
395 Crashes

55

Speed Limit on Urban Conventional Roadways (UC)

(Includes 2, 4, and 6 Lane Roads)

Traffic Safety Fundamentals

Handbook2008

55

Segments
18 Segments(Includes
20 Segments
2, 4, and 623Lane
Roads) 15 Segments
13 Miles
12 Miles
8 Miles
24 Miles
495 Crashes
403 Crashes
496 Crashes
1470 Crashes

Source: Mn/DOT UnPublished

2.38 2.32
Speed Limit on Urban Conventional Roadways (UC)

90 Segments
59 Miles
3750 Crashes

Change
MPH

185 Segments
128 Miles
7028 Crashes
15 Segments Statewide
10 Segments
Average = 4.0
13 Miles
12 Miles
495 Crashes
395 Crashes

MnDOT_C-24_1

50000
10000

Crash Rate Crash Rate

Highlights

Speed Zoning Studies

Nighttime (rural)
Daytime (rural)

MnDOT_C-24_1

Crash Involvement
Rate
Crash Involvement
Rate

50000

Source: Statistical
relationship between
vehicular crashes
and highway access
Report: MN/
RC199827

There are two basic types of speed zones in Minnesota:

1. Statutory speed limits established by the legislature 30 mph on
City Streets, 55 mph on Rural Roads, 65 mph on Rural Expressways, and
70 mph on Rural Interstates.
2. Speed zones established based on the results of an engineering study
of a particular roadway. The legislature has assigned the responsibility
for setting the speed limits in the zones to the Commissioner of
Transportation.
The premise underlying the establishment of speed limits is that most drivers
will select a safe and reasonable speed based on their perception of the
roadways condition and environment. This has lead to the practice of
conducting a statistical analysis of a sample of actual vehicle speeds as part
of a comprehensive engineering investigation.
The two primary performance measures are:
1. 85th percentile speed The speed below which 85% of the vehicles are
traveling.
2. 10 mph Pace the 10 mph range that contains the greatest number of
vehicles.
Experience has shown that the most effective speed limits are those that
are close to the 85th percentile speed and in the upper part of the 10
mph pace.
There are three important safetyrelated messages related to vehicle speeds
and speed limits:
1. Research demonstrates that roads with speed limits near the 85th
percentile speed have the lowest crash rates.
2. On urban roadways, crash rates have an inverse relationship with speed
limits (crash rates go down as speed limits increase). Crash rates have a
direct relationship with the number of access points along a road.
3. Artificially established speed limits have NEVER been successful at
changing behavior or reducing crashes.

C-27

Technology Applications
Highlights
The Technology

Display
Actual Speed

Static
Regulatory
Sign

Dynamic Speed
Monitoring (DSMD)
Sign

Flashes if
Over Limit

The Federal Highway Administration and Mn/DOT have invested in a

considerable amount of research regarding the use of new technology to
address traffic operations and safety deficiencies.

Advanced technologies have been successfully deployed to address

freeway traffic management, and a new generation of traffic signal
controllers and optical detectors are improving traffic flow on urban
arterials.

Research is currently underway at several universities, including the

University of Minnesota, to better understand factors contributing to
intersection crashes in order to develop new devices for assisting drivers
in selecting safe gaps at uncontrolled intersections, making safer turns at
controlled intersections, and providing additional warning when drivers
violate the intersection control.

The following examples of new devices have already been deployed:

Permanently
Mounted

Dynamic Mainline Warning Sign

Traffic Safety Fundamentals Handbook

2008

Missouri and North Carolina Department of Transportations use of

Dynamic Mainline warning signsInstead of a static intersection
warning sign, loop detectors on the stop controlled approaches
activate flashers on the mainline only when vehicles are present.
An initial safety review of two or more expressway intersections
found a 30 to 50% reduction in angle crashes following installation.

Dakota, Ramsey, and Washington Counties have deployed Dynamic

Speed Monitoring Display Signs in five speed transition zones in the
Minneapolis St. Paul Metropolitan Area. Before vs. After studies
have documented statistically significant speed reductions in the
range of 5 to 10 mph following installation.

C-28

NCHRP

VOLUME 17

L
NATIONA IVE
AT
COOPER
Y
HIGHWA
CH
RESEAR
M
PROGRA

T 500
REPOR

tion of the
Implementa
n
Guidance for
ay Safety Pla
ategic Highw
AASHTO Str

A Guide for
Volume 17:
ne Collisions
Zo
k
or
W
g
Reducin

Work Zones

Emphasis Area Objectives and Strategies

Objectives

Strategies

19.1 D Improve driver

compliance with work
zone traffic controls

19.1 D1 Enhance enforcement of traffic laws in work zones (T)

19.1 D2 Improve credibility of signs (E)
19.1 D3 Improve application of increased driver penalties in work zones (T)

19.1 E Increase
knowledge and
19.1 E1 Disseminate work zone safety information to road users (T)
awareness of work zones 19.1 E2 Provide work zone training programs and manuals for designers and field staff (T)
19.1 F Develop
procedures to effectively
manage work zones

19.1 F1 Develop or enhance agency-level work zone crash data system (T)
19.1 F2 Improve coordination, planning, and scheduling of work activities (T)
19.1 F3 Use incentive to create and operate safer work zones (T)
19.1 F4 Implement work zone quality assurance procedures (i.e., safety inspections or audits (T)

(P) = Proven; (T) = Tried; (E) = Experimental. A detailed explanation of (P), (T), and (E) appears in Section V. Several have
substrategies with different ratings.
Source: NCHRP Series 500 Reports, Vol. 17 A Guide for Reducing Work Zone Collisions

Highlights

Addressing crashes in work zones is one of AASHTOs Safety Emphasis Areas based on the fact that these crashes result in 1,000 fatalities and 40,000 injuries each year.

Minnesota averages around 1,600 crashes in work zones annually, with approximately 10 fatalities and over 700 injuries.

These statistics support the conclusion that crashes in work zones are over represented and that driving conditions in work zones differ from normal driving conditions.

Work zones can be a challenge for drivers because of a variety of unexpected conditions distractions, congestion, a greater demand for more precise navigation, etc.

A review of Minnesotas work zone crashes found that the most frequent type is a Rear End, the most severe type is a road departure (often involving an edge drop or uneven
pavement) and that hours of darkness are most at risk.

The strategies suggested in the NCHRP Series 500 Report, Volume 17 represent a comprehensive approach a coordinated effort by engineers, law enforcement
and educators.

From a highway agency perspective the key strategies involve design of work zones (have a plan consistent with the MNMUTCD and Field Manual), regular inspection and
maintenance of the devices (to make sure the are placed correctly and still relevant) and worker safety (adequately trained and wearing high visibility garments).

Concerns about traffic operations and safety has resulted in a new Federal rule on work zone safety and mobility, which Mn/DOT has also adopted as policy for all projects
on the State system and for State Aid projects that include Federal Funds. Basically, this new policy requires the preparation of a Work Zone Mobility Impact Assessment
(http://www.dot.state.mn.us/tecsup/tmemo/active/tm07/16t05.pdf) and the work zone management strategies (including traffic control, travel demand management and
public information) to mitigate impacts.

Traffic Safety Fundamentals

Handbook2008

C-29

Crash Reduction Factors

Highlights

Effectiveness
Countermeasure(s)

Crash
Type

Crash
Severity

Area
Type

Road
Type

Daily Traffic
Volume (veh/
day)

Ref.

Crash
Reduction
Factor/
Function

Std.
Error

Range
Low

Study Type

High

SIGNS
Implement sign
corrections to
MUTCD standards

Install chevron
signs on horizontal
curves

Install curve
advance warning
signs

Install curve
advance warning
signs (advisory
speed)

All

Injury

Urban

Local

15

10

Meta Analysis

All

PDO

Urban

Local

Meta Analysis

All

Fatal/
Injury

Rural

2-lane

38

20

All

All

15

35

All

All

64

All

All

15

20

All

All

15

35

All

All

15

50

All

Fatal/
Injury

38

10

All

Injury

30

71

Meta Analysis

16

Meta Analysis

Urban

Rural

Arterial
(Urban)

2-lane

All

PDO

All

All

15

30

All

Fatal

15

55

All

All

15

30

All

All

15

23

49

All

Injury

15

20

All

15

29

ROR

All

15

30

30

13

Meta Analysis

23

Meta Analysis

ROR

All

All

Injury

All

All

All

PDO

29

All

All

15

29

All

All

15

20

Source: FHWA-SA-07-015, September 2007

Traffic Safety Fundamentals

Handbook2008

Report No. FHWA-SA-07-015

U.S. Department of Transportation
Federal Highway Administration

September 2007

This document provides estimates of the crash reduction that

might be expected if a specific countermeasure is implemented,
based on the results contained in published research.

Crash reduction factors (CRFs) are provided for intersection

treatments, roadway departure strategies, and pedestrian
amenities.

In many cases, the Desktop Reference includes multiple CRFs

for the same countermeasure in order to suggest a range of
potential effectiveness. For example, installing chevron signs
on horizontal curves is expected to reduce all crashes by 20 to
64 percent.

These CRFs are a useful guide, but it remains necessary to

apply engineering judgment and to consider sitespecific
environmental, traffic volume, traffic mix, geometric
conditions, and operational conditions that will affect the
actual safety impact of any countermeasure.

In Minnesota, these CRFs are considered a supplement to

estimates of safety effectiveness derived from analyses of our
own crash records.

www.transportation.org/sites/safetymanagement/docs/
desktop%20reference%20complete.pdf

Simple
Before-After

Head-on

The Federal Highway

Administration has
published the most
comprehensive set of
crash reduction factors
Desktop Reference for
Crash Reduction Factors.

Desktop Reference
for
Crash Reduction Factors

C-30

Average Crash Costs

$6,800,000
$390,000
$ 121,000
$ 75,000
$ 12,000

Highlights

Per

Per

FATAL Crash

The costs shown were developed in 2008 by

Mn/DOT on a per crash basis for use in calculating
benefit/cost comparisons only. The costs include
economic cost factors and a measure of the value
of lost quality of life that society is willing to pay to
prevent deaths and injuries associated with motor
vehicle crashes. Costs originally published by the
FHWA on a per injury (and fatality) basis, were
utilized in the development.

Due to the very high cost for fatal crashes and the
effect this can have on the outcome of benefit/cost
analyses, it is the practice in Minnesota to value
fatal crashes as 2xSeverity A Crash ($780,000
per crash) unless there is a high frequency of fatal
crashes of a type susceptible to correction by the
proposed action.

Incapacitating Injury

SEVERITY B Crash

Per

Mn/DOT uses the following comprehensive crash

costs when computing the expected benefits
associated with roadway and traffic control
improvements.

SEVERITY A Crash

Per

Nonincapacitating Injury

SEVERITY C Crash

Possible Injury

PROPERTY
DAMAGE ONLY Crash
Per

Source: Developed by Mn/DOT Office of Traffic, Safety and Technology

Traffic Safety Fundamentals

Handbook2008

C-31

Crash Reduction Benefit/

Cost (B/C) Ratio Worksheet
HES
B/C
worksheet

Control T.H. /
Section Roadway
I-494

Beginning
Ref. Pt.

Location
Portland Ave to Nicollet Ave

Description of
Proposed Work

3+00.848

Ending
Ref. Pt.

State,
County, City
or Township

Study
Period
Begins

Study
Period Ends

4+00.357

Hennepin
Co.

1/1/2004

12/31/2006

2 Sideswipe
Same Direction

3 Left Turn Main Line

5 Right Angle 4,7 Ran off Road

8, 9 Head On/
Sideswipe -Opposite

Fatal
Personal Injury (PI)

Comparing the expected crash reduction benefits of a particular

safety countermeasure to the estimated cost of implementation is
an accepted analytical tool used in evaluating alternatives at one
location or to aid in the prioritization of projects across a system.

The basic concept is to give preference to the project(s) that

produced the greatest benefit for the least amount of investment.

The worksheet calculates benefits as the expected reduction in

crash costs on an annual basis and compares this value to the
annualized value of the estimated construction cost.

The methodology only accounts for benefits associated with

crash reduction. However, the process could be revised to also
account for other benefits such as improved traffic operations
(reduced delay and travel times).

It should be noted that benefit/cost analysis does not attempt to

account for all potential benefits associated with any particular
project since some economic and social benefits are very
difficult to quantify.

6, 90, 99

Direction

Pedestrian

Property
Damage

Construct Westbound auxiliary lane between Portland and Nicollet

Accident Diagram 1 Rear End

Codes

Study
Period:
Number of
Crashes

Highlights

Other

Total

F
A
B
C

PD

3
10

F
A
% Change
in Crashes

PI

*Recommend
using MnDOT's
% Change in
Crashes

B
C

-25%

PD

-25%

-25%

F
A
Change in
Crashes

PI

= No. of

crashes x
% change in
crashes

B
C

-0.75

PD

-1.75

-0.75
-0.75

Year (Safety Improvement Construction)

Project Cost (exclude Right of Way)

Study
Period:
Type of Change in
Crashes
600,000 Crash

Right of Way Costs (optional)

Traffic Growth Factor

3%

Capital Recovery
1. Discount Rate
2. Project Service Life (n)

-2.50

2013

4.5%
30

Annual
Change in
Crashes Cost per Crash Annual Benefit

0.47

B/C=

6,800,000

390,000

B= $

283,990

121,000

C= $

600,000

Using present worth values,

-0.75

-0.25 $

75,000

See "Calculations" sheet for

7,750 amortization.

PD

-2.50

-0.83 $

12,000

3,833

Total

Office of Traffic, Safety and

11,583 Operations
November 2007

Note: The Excel Spreadsheet File may be Downloaded from Mn/DOTs Website

Traffic Safety Fundamentals

Handbook2008

C-32

Typical Benefit/Cost Ratios

for Various Improvements

Source: FHWA, Highway Safety Evaluation System (April 14, 1999)

Rank

Construction Classification

B/C Ratio

Illumination

21.0

Highlights

Relocated Breakaway Utility Poles

17.2

Traffic Signs

16.3

Upgrade Median Barrier

13.7

The Federal Highway Administration has

documented the benefit/cost ratios for a variety of
typical safetyrelated roadway improvements.

New Traffic Signals

8.3

New Median Barrier

8.3

Remove Obstacles

8.3

Typical benefits/costs ranged from 1.9 for skid

overlays to 21.0 for illumination.

Impact Attenuators

7.8

Upgrade Guardrail

7.6

These benefits/costs should only be used as a guide

and not as the definitive expected value at any
particular location in Minnesota.

Benefits/costs in the range of 2 to 21 would likely

only be achieved at locations with crash frequencies
significantly higher than the expected values.

Mn/DOT funded safety research has documented

benefits/costs for a variety of safety projects,
including:
Street lighting at rural intersections (21:1)
Cable median barrier along freeways (10:1)
Access management (in the range of 3:1 to 1:1)

10

Upgraded Traffic Signals

7.4

11

Upgraded Bridge Rail

7.1

12

Sight Distance Improvements

7.0

13

Groove Pavement for Skid Resistance

5.6

14

Replace or Improve Minor Structure

5.2

15

Turning Lanes and Traffic Separation

4.4

16

New Rail Road Crossing Gates

3.9

17

Construct Median for Traffic Separation

3.3

18

New Rail Road Crossing Flashing Lights

3.2

19

New Rail Road Flashing Lights and Gates

3.0

20

Upgrade Rail Road Flashing Lights

2.9

21

Pavement Marking and Delineations

2.6

22

Flatten Side Slopes

2.5

23

New Bridge

2.2

24

Widen or Improve Shoulder

2.1

25

Widen or Modify Bridge

2.0

26

Realign Roadway

2.0

27

Overlay for Skid Treatment

1.9

Traffic Safety Fundamentals

Handbook2008

C-33

Lessons Learned Contents

D-1

Lessons Learned: Crash Characteristics

D-2

Lessons Learned: Safety Improvement Process

D-3

Lessons Learned: Traffic Safety Tool Box

Lessons Learned:
Crash Characteristics

At the National level the number of traffic related fatalities during the past 10 years is relatively flat - averaging between 42,000 and 43,000 deaths per year.

Over this same 10 year period, the trend in Minnesota is decidedly better the number of traffic related fatalities has declined at a rate approaching 3% per year and the
interim safety goal of getting under 500 traffic fatalities was achieved in 2006 (when 494 Minnesotans died in traffic crashes).

In 2006 the National fatality rate was 1.4 fatalities per 100 million vehicle miles traveled and the range was from 0.8 to 2.3. Minnesotas fatal crash rate was 0.9, which
was the second lowest in the country and the lowest of any state not in the northeast.

Fatal crashes in Minnesota are not distributed evenly across the State 70% of fatal crashes are in rural areas and the fatality rate on rural roads is more than 2.5 times the
rate in urban areas.

AASHTOs Strategic Highway Safety Plan suggested and the Federal Highway Administration has adopted a new national safety performance measure the number of
traffic fatalities.

Crashes are typically caused by a variety of factors, but the primary factor is driver behavior followed by roadway features and vehicle equipment failures.

The adoption of the new safety performance measure a focus on traffic fatalities has resulted in a better understanding of the fact that fatal crashes are different than
other less severe crashes. The most common type of crash is a rear end (28% of all crashes), however, the most common types of fatal crashes include; Run-off-road (34%),
Angle crashes (23%) and Head-on crashes (17%).

Fatal crashes are not evenly distributed across the population of drivers young drivers (under 20) represent about 7% of all drivers but are involved in almost 14% of fatal
crashes.

Most crashes occur on dry roads in good weather and during daylight conditions its a function of exposure. However, nighttime hours present a greater risk for severe
crashes 11% of all crashes occur during dark conditions but 26% of fatal crashes occur during hours of darkness.

Contrary to popular opinion, signalized intersections are only rarely safety devices. The average crash rate, severity rate and crash density is higher at signalized
intersections compared to the statistics for STOP controlled locations.

The most common types of intersection related crashes are Rear End and Right Angle. The installation of a traffic signal changes the crash type distribution increasing
Rear End crashes and reducing (but not eliminating) Right Angle crashes.

Crash rates on roadway segments are a function of location (rural vs. urban), design (conventional vs. expressway vs. freeway) and the degree to which access is managed.
Rural freeways and 2-lane roads have the lowest crash rates, urban minor arterials have the highest crash rates and rural county highways and township roads have the
highest fatal crash rates.

Urban crashes are predominantly two vehicle (Rear End and Right Angle) and rural crashes are predominantly single vehicle (Run-Off-Road and Deer Hits).

Within design categories of roads (rural 2-lane, urban 4-lane, expressway, etc.) the density of access can be used to predict crash rates segments with higher access
densities have higher crash rates in both rural and urban areas.

Traffic Safety Fundamentals

Handbook2008

D-1

Lessons Learned:
Safety Improvement Process

Mn/DOTs current Strategic Highway Safety Plan (SHSP) was approved in September, 2007. The Plan was data driven, comprehensive (addressed the four Safety Es),
systematic (considered all roads), identified a new safety performance measure (fatal and severe injury crashes) and established a new interim safety goal (400 or fewer
fatalities by 2010).

The SHSP identified seven Safety Emphasis Areas for Minnesota in two categories Driver Behavior (safety belts, alcohol, speeding and young drivers) and Infrastructure
(intersection, run-off-road and head-on crashes).

In urban areas the primary factors associated with fatal crashes are intersections and speeding and rural areas the primary factors are safety belts, alcohol and
road departures.

A comprehensive safety improvement process includes both a Black Spot analysis focused on reactive implementation of safety strategies and a system wide analysis
focused on proactively implementing generally low cost safety strategies broadly across an agencies system of roads.

Three alternative methods are suggested for identifying Black Spots the annual number of crashes at a given location, the crash rate or the critical crash rate. Each
method has advantages and disadvantages. Documenting the number of crashes annually is the easiest from a data gathering perspective; however, it has no ability to
account for differences in expected crash values based on type of intersection control or roadway design. The critical crash rate method is the most challenging to use
because of the need for comprehensive crash statistics for both individual locations and the entire system; however, it effectively accounts for random nature of crashes
and is the most statistically reliable.

The recommended analytical method for conducting a detailed study of an individual location involves comparing the Actual crash characteristics to the Expected
characteristics and then evaluating the differences. It is important to note that the expected crash frequency of any given location is never zero.

Of the three traditional methods for identifying hazardous locations (number of crashes, crash rate and critical crash rate), the Critical Crash Rate is the most statistically
reliable, but this is also the most data intensive method. However, the use of any method is better than not conducting a periodic safety inventory.

The single most important practice to support improving safety at the local level is for agencies to dedicate a portion of their annual capital improvement program to
implementing low-cost safety strategies on their system.

Traffic Safety Fundamentals

Handbook2008

D-2

Lessons Learned:
Traffic Safety Tool Box

Current traffic safety tool boxes are better stocked and include a more comprehensive set of safety strategies as a result of recent efforts by NCHRP (the Series 500 ReportsImplementation of AASHTOs Strategic Highway Safety Plan) and FHWA (Report No. FHWA-SA-07-015 Desktop Reference for Crash Reduction Factors).

The NCHRP Reports include 22 volumes documenting over 600 safety strategies dealing with all four safety Es Education, Enforcement, Engineering and Emergency
Services. The NCHRP Reports categorize strategies as Proven (effective at reducing crashes), Tried or Experimental. Examples of Proven strategies include:

Street Lights

Access Management

Roadside Safety Initiatives

Roundabouts

Cable Median Barrier

Left turn Lanes (on urban arterials)

Traffic Signal Optimization

A variety of traditional strategies that were once thought to be effective are considered to be Tried, because there are no statistically reliable studies documenting
effectiveness. These Tried strategies include; Installing Traffic Signals, Overhead Flashers (at rural intersections) and the installation of Transverse Rumble Strips (on the
approach to STOP controlled intersections).

Match the magnitude of the solution to the magnitude of the problem.

Consider interim measures when implementation of the ultimate solution would take years to implement.

The most effective safety strategies usually include elements from each of the four safety E'sEducation, Enforcement, Engineering and Emergency Services.

Traffic Safety Fundamentals

Handbook2008

D-3