NCHRP Report 812
SIGNAL
TIMING
MANUAL
Second Edition
Acknowledgments
Team Members & Panel Members
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•
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•
•
•
•
•
•
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Tom Urbanik, Kittelson & Associates, Inc.
Alison Tanaka, Kittelson & Associates, Inc.
Bailey Lozner, Kittelson & Associates, Inc.
Eric Lindstrom, Kittelson & Associates, Inc.
Kevin Lee, Kittelson & Associates, Inc.
Shaun Quayle, Kittelson & Associates, Inc.
Scott Beaird, Kittelson & Associates, Inc.
Shing Tsoi, Kittelson & Associates, Inc.
Paul Ryus, Kittelson & Associates, Inc.
Doug Gettman, Kimley-Horn and
Associates, Inc.
• Srinivasa Sunkari, Texas A&M
Transportation Institute
• Kevin Balke, Texas A&M Transportation
Institute
• Darcy Bullock, Purdue University
NCHRP Report 812
• Eddie Curtis, Federal Highway
Administration
• Richard Denney, Federal Highway
Administration
• Woody Hood, Maryland State Highway
Authority
• Peter Koonce, City of Portland, Oregon
• Susan Langdon, Savant Group,
Richardson, Texas
• Mark Luszcz, Delaware Department of
Transportation
• Doug Noble, Institute of Transportation
Engineers
• Paul Olson, Federal Highway Administration
• Bill Shao, City of Los Angeles, California
• Aleksandar Stevanovic, Florida Atlantic
University
• Jim Sturdevant, Indiana Department of
Transportation
2
Acknowledgments
Focus Group Participants & Outside Reviewers
• Nader Ayoub, Iteris, Austin, Texas
• Don Cashdollar, Florida Department of
Transportation
• Larry Colclasure, Texas Department of
Transportation
• John Deskins, City of Kennewick,
Washington
• Hazem El-Assar, Orange County, Florida
• Chen Hsu, Virginia Department of
Transportation
• Ken Jacobs, Pinellas County, Florida
• Sage Kamiya, Sarasota/Manatee County,
Florida
• Mike Kinney, Montgomery County, Maryland
• Rob Klug, Clark County, Washington
• Aii Mozdbar, City of Austin, Texas
• Eric Nelson, Advanced Traffic Solutions,
Houston, Texas
NCHRP Report 812
• Keith Orr, City of Portland, Oregon
• Keith Riniker, Sabra Wang, Baltimore,
Maryland
• Tiffany Slaughter, Oregon Department of
Transportation
• Mark Titus, City of Richardson, Texas
• Nhan Vu, Virginia Department of
Transportation
• Charlie Wetzel, Seminole County, Florida
• Paul Zebell, City of Portland, Oregon
• John Black, City of Richardson, Texas
• Denny Eyler, SRF Consulting, Plymouth,
Minnesota
• Airton Kohls, University of Tennessee
• Michael Kyte, University of Idaho
• Wasim Raja, District of Columbia
Department of Transportation
• Robert Saylor, City of Richardson, Texas
3
Focus for the Second Edition
• Focused information written for new practitioners and
those desiring a better understanding of signal timing
fundamentals.
• Addition of four new chapters for more advanced users.
• Material organized so that it is presented once and
referenced as needed elsewhere in the document.
• Inclusion of essential information only (i.e. no “nice to
know” information).
• References to other documents, instead of repeated
material.
• Expanded use of graphics to aid in the explanation of
more complex topics.
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5
SIGNAL TIMING
FUNDAMENTALS
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CHAPTER 1
Introduction
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Chapter 1. Introduction
The second edition has
an increased focus on
signal system users and
their priorities, and
introduces an outcome
based approach to
signal timing.
NCHRP Report 812
• Focus for the Second
Edition
• Introduction to the
Outcome Based
Process
• STM2 Organization
8
CHAPTER 2
Signal Timing Program
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Chapter 2. Signal Timing Program
Signal timing programs
assure that signal timing
parameters are
appropriate over the life
of the traffic signal
system, by monitoring all
aspects of traffic signal
implementation,
operations, and
maintenance consistent
with community needs.
NCHRP Report 812
• Leadership
• Self-Assessment and
Evaluation
• Funding Mechanisms
• Training Programs
• Public Involvement
and Outreach
• Benefits of Regional
Signal Timing
Programs
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CHAPTER 3
Signal Timing Concepts
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Chapter 3. Signal Timing Concepts
This chapter provides an
overview of signal timing
basics, organized using
the outcome based
process. The outcome
based process is a
modern approach to
signal timing that
encourages practitioners
to consider all system
users.
NCHRP Report 812
• Common Signal
Components and
Interactions
• Basic Signal Controller
Concepts
• Outcome Based
Process
• Data Collection
• Operational Objectives
and Performance
Measures
12
Chapter 3 introduces common signal components,
interactions, and signal controller concepts…
NCHRP Report 812
Chapter 3. Signal Timing Concepts
13
Followed by an explanation of the steps in the outcome based process.
NCHRP Report 812
Chapter 3. Signal Timing Concepts
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NCHRP Report 812
Chapter 3. Signal Timing Concepts
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CHAPTER 4
Signal Design
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Chapter 4. Signal Design
Effective signal timing
requires appropriate
signal design. This
chapter discusses signal
design elements that
directly influence signal
timing.
NCHRP Report 812
• Detection
• Signal Cabinet
Equipment
• Displays
• Signalized System
Design
• Lessons Learned
17
Chapter 4 describes the relationship between detectors,
signal cabinet equipment, and displays…
NCHRP Report 812
Chapter 4. Signal Design
18
Followed by detailed information about detection
(including decision zone protection)…
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Chapter 4. Signal Design
19
Detailed information about signal cabinet equipment…
NCHRP Report 812
Chapter 4. Signal Design
20
And detailed information about displays for vehicles,
pedestrians, bicycles, and transit users…
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Chapter 4. Signal Design
21
Concluding with a description of communications equipment between signals.
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Chapter 4. Signal Design
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BASIC SIGNAL
SYSTEMS
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CHAPTER 5
Introduction to Timing Plans
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Chapter 5. Introduction to Timing Plans
This chapter is part of a
three-part series about
developing signal timing
plans. It describes basic
signal timing concepts
that a practitioner should
understand before
defining signal timing
values.
NCHRP Report 812
• Movements and
Phases
• Ring-and-Barrier
Concept
• Left-Turn Phasing
• Overlaps
• Detector and Load
Switch Assignments
• Critical Movement
Analysis
• Software Models and
Considerations
25
Chapter 5 explains movement and phase numbering…
NCHRP Report 812
Chapter 5. Introduction to Timing Plans
26
Using various phasing examples…
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Chapter 5. Introduction to Timing Plans
27
Followed by an explanation of ring-and-barrier diagrams…
NCHRP Report 812
Chapter 5. Introduction to Timing Plans
28
Using various phasing examples…
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Chapter 5. Introduction to Timing Plans
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Concluding with step-by-step instructions for critical movement analysis...
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Chapter 5. Introduction to Timing Plans
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Cycle Length
(Seconds)
Number
of Cycles
Per Hour
Lost Time
Per Cycle
1
(Seconds)
Effective
Green Time
Per Cycle
(Seconds)
60
70
80
90
100
110
120
60
51
45
40
36
33
30
20
20
20
20
20
20
20
40
50
60
70
80
90
100
Number
of Vehicles
2
Per Cycle
Maximum
Number
of Vehicles
2
Per Hour
16
19
23
27
31
35
39
933
1000
1050
1089
1120
1145
1167
1
This lost time assumes that the intersection is operating with eight phases (four in each ring) with 5 seconds of
lost time per phase. The lost time will be less at an intersection with fewer phases.
2 The number of vehicles that can be accommodated under the various cycle lengths was calculated assuming a
headway of 2.5 seconds per vehicle, which is generally conservative for urban/suburban environments.
Including how critical movements relate to cycle length…
NCHRP Report 812
Chapter 5. Introduction to Timing Plans
31
Signal Timing
Parameter
Phase Sequence
Chapter 5
Reference
5.1.1 Movement and
Phase Numbering
5.1.2 Ring-and-Barrier
Concept
5.1.3 Left-Turn Phasing
5.1.4 Overlaps
Inputs
Minimum Green
Passage Time
Minimum Gap
Chapter 7
Reference
7.2.6 Bandwidth
7.6.1 Phase Sequence
6.1.3 Minimum Green
6.1.4 Maximum Green
Maximum Green
Yellow Change
Red Clearance
Leading/Lagging
Left Turns
Chapter 6
Reference
7.4.3 Splits Guidance
7.4.4 Force-Offs Guidance
6.1.1 Yellow Change
6.1.2 Red Clearance
5.1.3 Left-Turn Phasing
7.2.6 Bandwidth
7.6.1 Phase Sequence
6.1.5 Passage Time (Unit
Extension or Gap
Time)
6.1.5 Passage Time (Unit
Extension or Gap
Time)
As well as information about software models and considerations.
NCHRP Report 812
Chapter 5. Introduction to Timing Plans
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EXAMPLE
Trailing Overlaps
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Trailing Overlaps Example
A trailing overlap
continues timing after
the parent phase ends.
It is an overlap
application that is
commonly used at
closely-spaced
intersections.
NCHRP Report 812
• Trailing Overlaps
Overview
• Trailing Overlaps Ringand-Barrier Diagram
34
Trailing Overlaps Example
Trailing Overlaps Overview
REFERENCE PAGES
5-11 TO 5-16
NCHRP Report 812
Section 5.1.4 Overlaps
35
Trailing Overlaps Example
Trailing Overlaps Ring-and-Barrier Diagram
REFERENCE PAGES
5-11 TO 5-16
NCHRP Report 812
Section 5.1.4 Overlaps
36
CHAPTER 6
Intersection/Uncoordinated Timing
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Chapter 6. Intersection/Uncoordinated Timing
This chapter provides
guidance on basic signal
timing parameters used
at uncoordinated
intersections (i.e.
intersections running in
“free” operation).
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NCHRP Report 812
Yellow Change
Red Clearance
Minimum Green
Maximum Green
Passage Time
Pedestrian Intervals
Dual Entry
Recalls and Memory
Modes
Detector Delay
Detector Extend Time
Detector Switching
Time-of-Day Plans
38
Typical Values for Maximum Green
Phase Type
Through
Left Turn
Facility Type
Maximum Green (Seconds)
Major Arterial (> 40 mph)
Major Arterial (≤ 40 mph)
Minor Arterial
Collector, Local, or Driveway
Any
50 to 70
40 to 60
30 to 50
20 to 40
15 to 30
Typical Values for Passage Time
Detection Zone
Length (Feet)
25
6
20
40
60
80
2.3
1.9
1.4
0.8
0.3
Passage Time (with a Headway of 3 Seconds) (Seconds)
Posted Speed (MPH)
30
35
40
45
50
2.4
2.1
1.6
1.2
0.7
2.5
2.2
1.8
1.4
1.1
2.6
2.3
2.0
1.6
1.3
2.6
2.4
2.1
1.8
1.5
2.6
2.5
2.2
1.9
1.6
55
2.7
2.5
2.3
2.0
1.8
Chapter 6 provides guidance on signal timing parameters
and typical values (e.g., maximum green, passage time)…
NCHRP Report 812
Chapter 6. Intersection/Uncoordinated Timing
39
As well as an explanation of how timers work and can be applied.
NCHRP Report 812
Chapter 6. Intersection/Uncoordinated Timing
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EXAMPLE
Passage Time
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Passage Time Example
Passage time (also
called unit extension or
gap time) is a parameter
that can be used to
terminate the current
phase when a gap in
traffic is identified.
NCHRP Report 812
• Passage Time
Example Application
• Passage Time and
Flow Rate
Relationship
42
Passage Time Example
Passage Timer Counts Down But Minimum Green Timer Has Not Expired
REFERENCE PAGES
6-10 TO 6-16
NCHRP Report 812
Section 6.1.5 Passage Time (Unit Extension or Gap Time)
43
Passage Time Example
Passage Timer Resets with Vehicle Actuation
REFERENCE PAGES
6-10 TO 6-16
NCHRP Report 812
Section 6.1.5 Passage Time (Unit Extension or Gap Time)
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Passage Time Example
Passage Timer Counts Down When Detector is Unoccupied
REFERENCE PAGES
6-10 TO 6-16
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Section 6.1.5 Passage Time (Unit Extension or Gap Time)
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Passage Time Example
Passage Timer Expires and Phase Gaps Out
REFERENCE PAGES
6-10 TO 6-16
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Section 6.1.5 Passage Time (Unit Extension or Gap Time)
46
Passage Time Example
Phase Transitions to Yellow and Red Regardless of Vehicle Actuations
REFERENCE PAGES
6-10 TO 6-16
NCHRP Report 812
Section 6.1.5 Passage Time (Unit Extension or Gap Time)
47
Passage Time Example
Passage Time and Flow Rate Relationship
REFERENCE PAGES
6-10 TO 6-16
NCHRP Report 812
Section 6.1.5 Passage Time (Unit Extension or Gap Time)
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CHAPTER 7
System/Coordinated Timing
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Chapter 7. System/Coordinated Timing
Coordination allows
signals to operate as a
group, thereby
synchronizing
movements and allowing
for better progression.
This chapter explains
how basic signal timing
parameters can be used
in conjunction with
coordinated features.
NCHRP Report 812
• Application of a Coordinated
System
• Time-Space Diagram
• Coordinated Phases
• Cycle Length
• Splits
• Force-Offs
• Permissives
• Yield Point
• Pattern Sync Reference
• Offset Reference Point
• Offsets
• Pedestrian Timing and Walk
Modes
• Actuating the Coordinated
Phase
• Transition Logic
• Complexities
50
Chapter 7 describes time-space diagram basics…
NCHRP Report 812
Chapter 7. System/Coordinated Timing
51
And uses them to explain how vehicles move within a coordinated system…
NCHRP Report 812
Chapter 7. System/Coordinated Timing
52
As well as coordinated signal timing parameters…
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Chapter 7. System/Coordinated Timing
53
Followed by information about coordination considerations
(e.g., actuating the coordinated phase) and complexities.
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Chapter 7. System/Coordinated Timing
54
CHAPTER 8
Implementation and Maintenance
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Chapter 8. Implementation and Maintenance
This chapter describes
taking final timing plans
through implementation
and to the point where
they must be monitored
and maintained.
Maintenance ensures
that the signal timing will
continue to operate at
the level expected by
the operating agency
and general public.
NCHRP Report 812
• Transfer Plans from
Office to Field
• Field Observations
and Adjustments
• Performance Studies
• Monitoring
• Maintenance
• Staffing Needs
56
Chapter 8 provides information about various methods for
transferring signal timing plans from the office to the field…
NCHRP Report 812
Chapter 8. Implementation and Maintenance
57
Field Observation
□
Long minor street delay
Long major street leftturn delay
□
□
□
□
□
□
□
Vehicle queuing
Vehicle platoons arriving
on red
□
□
□
□
□
□
□
□
□
Potential Adjustments
Redistribute green time between major street phases and minor street phases
(e.g., minimum green, maximum green, or splits).
Review cycle length.
Review passage settings for major street phases.
Consider actuating the coordinated phase(s).
Redistribute green time to major street left-turn phases (e.g., minimum green,
maximum green, or splits).
Review passage settings for major street through phases and minor street
phases.
Consider left-turn phase sequence.
Redistribute green time to phases with queuing (e.g., minimum green,
maximum green, or splits).
Review cycle length.
Review offsets.
Review passage settings for other phases (not experiencing queuing).
Consider left-turn phase sequence.
Consider phase re-service.
Review offsets.
Consider left-turn phase sequence.
Review cycle length.
Review upstream intersections for early return to green and possible offset
adjustment.
As well as guidance for adjusting signal timing based on field observations…
NCHRP Report 812
Chapter 8. Implementation and Maintenance
58
Signal
Operations
Category
□
Example Public
Service Requests
Not Getting a
Green
□ “My movement is
not getting a
green.”
Short Green
□ “My movement
gets a green, but
the green is too
short.”
Potential Questions to Identify a Solution
□ Is the intersection part of a coordinated system (that dedicates
time to certain phases for progression)?
□ Have the detectors been damaged?
□ Is the stopping point well defined (so that vehicles will stop
over the detectors)?
□ Is the detection zone appropriate (e.g., large enough to detect
vehicles in a wide approach, sensitive enough to detect
bicycles)?
□ How are the detectors being operated? Is the non-locking
setting being used when needed?
□ Was preemption active?
□ If the intersection is part of a coordinated system, is the
correct plan running?
□ Are the splits appropriate and customized for the intersection?
□ If the particular phase is on recall, are the detectors working
properly?
□ Was preemption active?
□ If it is a multi-lane approach, is a lane temporarily out of
service due to construction or incomplete snow plowing?
□ Is the approach on a steep grade, where a slippery road could
affect performance?
Followed by information about monitoring and maintaining
signals (e.g., responding to public service requests).
NCHRP Report 812
Chapter 8. Implementation and Maintenance
59
ADVANCED SYSTEMS
AND APPLICATIONS
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CHAPTER 9
Advanced Signal Systems
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Chapter 9. Advanced Signal Systems
Advanced signal
systems are able to
make signal timing
adjustments based on
detection information,
thus modifying
operations during
varying traffic flow
conditions.
NCHRP Report 812
• Systems Engineering
• Advanced
Coordination Features
• Traffic Responsive
Plan Selection
Systems
• Adaptive Signal
Control Technology
Systems
62
CHAPTER 10
Preferential Treatment
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Chapter 10. Preferential Treatment
Preferential treatment is
an application that can
be used at signalized
intersections to adjust
operations in favor of
particular users.
NCHRP Report 812
•
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Detection Requirements
Signal Timing Strategies
Strategic Recovery
Data Logging
Advancements
Preemption Settings
Priority Settings
Considerations for Rail,
Emergency Vehicles,
Transit, and Trucks
64
Chapter 10 gives an overview of signal
timing strategies (e.g., sequence change)…
NCHRP Report 812
Chapter 10. Preferential Treatment
65
Followed by information about advanced preferential treatment options…
NCHRP Report 812
Chapter 10. Preferential Treatment
66
Concluding with specific details about preferential
treatment for rail, emergency vehicles, transit, and trucks.
NCHRP Report 812
Chapter 10. Preferential Treatment
67
CHAPTER 11
Special Conditions
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Chapter 11. Special Conditions
For special conditions,
alternative signal timing
may be required to
maintain operations.
NCHRP Report 812
• Weather Events
• Traffic Incidents
• Planned Special
Events
69
CHAPTER 12
Oversaturated Conditions
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Chapter 12. Oversaturated Conditions
Although the issue of
oversaturation is often
not resolvable solely
through new signal
timing, there are several
mitigation strategies that
can be applied to
improve overall system
performance and
increase short-term
capacity.
NCHRP Report 812
• Symptoms of
Oversaturation
• Maximizing
Intersection
Throughput
• Queue Management
• Mitigation Strategies
71
Chapter 12 provides information about oversaturation symptoms
(e.g., overflow queue, spillback, blocking, and starvation)…
NCHRP Report 812
Chapter 12. Oversaturated Conditions
72
Followed by mitigation strategies, specifically for maximizing
intersection throughput and queue management.
NCHRP Report 812
Chapter 12. Oversaturated Conditions
73
EXAMPLE
Symptoms of Oversaturation
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Symptoms of Oversaturation
Oversaturated
conditions can be
identified using several
common symptoms.
Oversaturation can be
challenging because
these symptoms often
occur in combination.
NCHRP Report 812
•
•
•
•
•
Overflow Queue
Approach Spillback
Storage Bay Spillback
Storage Bay Blocking
Mitigation Strategies
for Oversaturated
Conditions
75
Symptoms of Oversaturation Example
Overflow Queue
REFERENCE PAGES
12-2 TO 12-4
NCHRP Report 812
Section 12.1 Symptoms of Oversaturation
76
Symptoms of Oversaturation Example
Approach Spillback
REFERENCE PAGES
12-2 TO 12-4
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Section 12.1 Symptoms of Oversaturation
77
Symptoms of Oversaturation Example
Storage Bay Spillback
REFERENCE PAGES
12-2 TO 12-4
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Section 12.1 Symptoms of Oversaturation
78
Symptoms of Oversaturation Example
Storage Bay Blocking
REFERENCE PAGES
12-2 TO 12-4
NCHRP Report 812
Section 12.1 Symptoms of Oversaturation
79
Symptoms of Oversaturation Example
Mitigation Strategies for Oversaturated Conditions
Operational
Objective
Type of
System
Mitigation Strategy
Split Reallocation
Individual
Intersection(s)
Cycle Length Increase
Operation of CloselySpaced Intersections
on One Controller
Phase Sequence
Modification for
1
Left Turns
Maximize
Intersection
Throughput
Arterial
Preemption Flushing
(“Green Flush”)
Alternative Timing
Plan Flushing
Green Extension
Individual
Intersection(s)
Phase Re-Service
Phase Truncation
Simultaneous Offsets
Manage
Queues
Negative Offsets
Arterial
Offsets to Prevent
Queue Spillback
Offsets to Prevent
Starvation
Network
Maximize
Intersection
Throughput
and Manage
Queues
REFERENCE PAGES
12-5 TO 12-21
NCHRP Report 812
Metering (Gating)
Adaptive Control
All
Combination of
Mitigation Strategies
Definition
Reallocating split time from under-saturated
phases to oversaturated phases.
Adding split time to oversaturated phases without
reducing split time for minor movements,
effectively increasing the cycle length.
Operating two intersections using one controller,
allowing close coordination.
Changing the phase sequence to lead or lag left
turns, increasing the bandwidth for progressing
platoons.
Progressing oversaturated movements by placing
calls from downstream intersections to upstream
intersections.
Using a timing plan to increase the cycle length
and give the majority of the green time to the
oversaturated phases.
Adding green time to a phase when a detector
exceeds a defined threshold of occupancy.
Serving an oversaturated phase twice during the
same cycle.
Termination of a green interval (despite demand)
when there is minimal to no flow over a detector.
Setting offset to zero between intersections, so
that queues move simultaneously.
Starting the green interval earlier at downstream
intersections to allow the downstream queue to
dissipate before upstream vehicles arrive.
Choosing offsets that allow the downstream
queue to clear before the upstream vehicles reach
the end of the downstream queue.
Choosing offsets that ensure the first released
vehicle at the upstream intersection joins the
discharging queue as it begins to move.
Impeding traffic at appropriate upstream points
to prevent traffic flow from reaching critical levels
at downstream intersections.
Applying detection data and adaptive signal
control algorithms to adjust signal timing.
Combining mitigation strategies and/or using
them in sequence throughout the oversaturated
period.
Section 12.3 Mitigation Strategies for Oversaturated Conditions
80
GLOSSARY
180+ Terms Defined
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