The National Academies

NCHRP 03-118 [Final]

Decision-Making Guide for Traffic Signal Phasing

  Project Data
Funds: $600,000
Research Agency: VHB
Principal Investigator: Christopher Daily
Effective Date: 8/13/2015
Completion Date: 8/31/2019

The objective of this research was to develop an engineering decision-making guide that incorporates both safety and operational impacts in evaluating traffic signal phasing alternatives for conventional intersections. NCHRP Web-Only Document 284, Decision-Making Guide for Traffic Signal Phasing, is available at https://www.trb.org/main/blurbs/181114.aspx.
Examples of Signal Phasing Alternatives that are addressed:
  • Left Turns (Protected Only v. Protected/Permitted v. Permitted Only, Leading v. Lagging, Split Phasing, Changes in phasing based on time of day or traffic conditions, Treatment of multiple left-turn lanes)
  • Right Turns (Overlaps with complementary left turns, Treatment of dual right turn lanes)
  • Pedestrians (Concurrent v. Exclusive, Leading Pedestrian Indication)
  • Interactions (Elimination of permitted left turns and right turns on a conflicting pedestrian actuation, Conflicts between U-Turns and Right Turns)

The FHWA has identified intersections as one of four primary focus areas for improving safety and reducing crashes. In the United States, it is estimated that signalized intersections comprise less than 10 percent of the total number of intersections; but more than 30 percent of intersection fatalities occur at signalized intersections. One of the most important factors impacting both the safety and operations at a signalized intersection is signal phasing (the order and manner in which movements are served by a traffic signal). Little research has been done in recent years related to the safety and operational aspects of signal phasing. Although there is some guidance in national manuals (such as the FHWA Signal Timing Manual), much of the information is based on rules-of-thumb with limited empirical underpinning. Selection of an appropriate signal phasing, given the prevailing conditions, can have the benefits of improving safety, decreasing delay, reducing congestion, and reducing emissions.

Task 1. Amplified Work Plan and Kickoff Meeting. The objective of this task is to develop the amplified work plan and conduct a kickoff meeting with the Panel to discuss the objectives of the study and agree on the overall technical approach and schedule.
Task 2. Review of Literature and Current Practices. The objective of this task is to review relevant literature and current traffic signal phase selection practices to help guide the study design and data collection.
Task 3. Identification of Participating Agencies. The objective of this task is to identify potential study areas.
Task 4. Study Design. The objective of this task is to develop methodologies to quantify the safety and operational impacts of decisions on signal phasing alternatives.
Task 5. Data Collection Plan. The objective of this task is to develop plans to guide the collection of safety and operational data. The data collection plans are somewhat dynamic and may be adjusted to meet the desires of the Panel and address new and novel topics as they surface during the project.
Task 6. Preliminary Outline of Guidelines. The objective of this task is to devlop a preliminary outline of the guidelines.
Task 7. Interim Report and Panel Meeting. The objective of this task is to document the findings of the first six tasks in an interim report, present the report to the Panel, and receive feedback on the proposed framework for subsequent tasks.
Task 8. Data Collection. The objective of this task is to implement the approved data collection plan developed in Task 5.
Task 9. Analysis. The objective of this task is to comprehensively analyze the data collected in Task 8, following the study designs developed in Task 4 and approved by the Panel, which will result in quantification of the impacts of traffic signal phase modes and sequencing on the safety and operational performance measures of interest.
Task 10. Assess Results. The objective of this task is to compare the results of the safety and operational analysis to provide guidance on how changes in operational measures might be balanced against changes in safety.
Task 11. Treatment Costs. The objective of this task is to develop cost estimates for implementing various strategies related to new or modified vehicle or pedestrian phasing at signalized intersections.
Task 12. Phase Selection Guidelines. The objective of this task is to develop a user-friendly guide that will assist traffic signal engineers in state and local agencies in selecting optimal signal phasing strategies and plans that will focus on improving safety and traffic operations for all users.
Task 13. Final Report and Deliverables. The objective of this task is to prepare the final report and deliverables.

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