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Traffic Engineering for Intersections

This document provides an overview of unsignalized intersection types including two-way stop control (TWSC), all-way stop control (AWSC), and roundabouts. It discusses the methodology, inputs, and outputs for calculating level of service using the Highway Capacity Manual (HCM) methods. For TWSC, the document outlines the priority rules, critical gap, follow-up time, and capacity calculations. It also notes considerations for upstream signals, two-stage gap acceptance, and flared approaches. For AWSC, it describes the theoretical operation patterns and configuration. Control delay is calculated using a probability of conflict. The document states SIDRA is recommended over HCM for roundabout analysis.

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Esra'a Alhaj
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323 views28 pages

Traffic Engineering for Intersections

This document provides an overview of unsignalized intersection types including two-way stop control (TWSC), all-way stop control (AWSC), and roundabouts. It discusses the methodology, inputs, and outputs for calculating level of service using the Highway Capacity Manual (HCM) methods. For TWSC, the document outlines the priority rules, critical gap, follow-up time, and capacity calculations. It also notes considerations for upstream signals, two-stage gap acceptance, and flared approaches. For AWSC, it describes the theoretical operation patterns and configuration. Control delay is calculated using a probability of conflict. The document states SIDRA is recommended over HCM for roundabout analysis.

Uploaded by

Esra'a Alhaj
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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You are on page 1/ 28

CE 784 Special Topics in Transportation Engineering

Dr. Bashar Al-Omari

1 B- Un-Signalized Intersections

1
Un-signalzied Intersection Major Types

Two Way Stop (TWS), All Way Stop (AWS), & Roundabouts

Level of Service (LOS)

2
A. Two Way Stop Control (TWSC)

Concept

depends on gap acceptance method which relies


on:
• Size and distribution of available gaps in the
major traffic stream
• Acceptance of gaps by minor street drivers,
• Priority of various movements.

3
Methodology

4
Inputs

•Geometry (# of lanes, use of lanes: shared /


exclusive, channelization, median type and
storage, approach grades, flared approaches
on minor streets).

•Traffic Volumes by movement, HV %, and


PHF

•Pedestrian volumes

•Major street signal data (random arrivals only


5 if signal > 400 m away)
Priority of Streams & Their Ranks

• Priority of streams and their ranks: (Exhibit 17-3)

• Convention: subscripts 1- 6 for major,


7-12 for minor,
13-16 for pedestrians.

• Movements 2, 5, 15 and 16 have the absolute


priority and do not give way to any other
movements.

• Conflicting Traffic for major (left turns), and minor


(right, through and left turns): (Exhibit 17-4)
6
7
8
9
10
Critical Gap: is the minimum time interval in the major street
traffic stream that allows intersection entry for one minor street
vehicle (equation 17-1).

11
12
Follow up Time: is the time between the departure of one
vehicle from the minor street and the departure of the next
vehicle using the same major street gap, under a condition of
continuous queuing on the minor street (equation 17-2).

13
Potential Capacity: for each movement is calculated
using equation 17-3

14
Movement Capacity:

reducing potential capacity for each movement


due to impedance by higher rank movements:

Movement Capacity=Potential Capacity * Capacity Adj. Factor

15
Shared Lane Capacity: the procedure assumes that each
movement has an exclusive lane. If shred lanes exist, then
their capacity should be adjusted according the percentages of
movement volumes (equation 17-15 for minor and 17-16 for
major).

16
17
• Upstream signals: if close signals exist, their
platooning effect must be considered. HCM has a
special procedure for that purpose.

• Two Stage Gap Acceptance: If exist, their effect must


be considered.

• Flared Minor Street Approaches: If exist, their effect


must be considered

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19
20
Control Delay

21
Approach and Intersection Delays

22
B. All Way Stop Control (AWSC)

Theoretical Operation Patterns

• two phases at two lane streets

• four phases at multi-lane streets

• choice between 2 & 4 phases depends on


the complexity of intersection geometry and
proportion of turning movements.

23
24
AWS Configuration

25
Methodology
The HCM uses a theoretical procedure for calculating the
probability of degree of conflict (between subject, conflicting &
opposing movements) and then Control Delay is calculated
using the following equation:

26
C. Roundabouts

HCM uses an approximate procedure for the analysis


of Roundabouts. (SIDRA is recommended)

27
C. Roundabouts

28
(SIDRA is Better Than HCS)

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