The Federal Highway Administration (FHWA) Traffic Signal Timing Manual (STM) has been the most widely accepted reference across the traffic signal timing field. Since the release of the second edition in 2015 (STMv2), there have been significant advances in signal timing research and practices, and several NCHRP and FHWA initiatives have been implemented.
· NCHRP Project 03-125, “Evaluation of Change and Clearance Intervals Prior to the Flashing Yellow Permissive Left-Turn Indication” evaluates change and clearance intervals prior to flashing yellow arrow (FYA).
· NCHRP Research Report 954: Performance-Based Management of Traffic Signals compiles the best available information on automated traffic signal performance measures and management strategies for traffic signal operations.
· NCHRP Web-only Document 284: Decision-Making Guide for Traffic Signal Phasing provides guideline for traffic signal phasing.
· NCHRP Research Report 969: Traffic Signal Control Strategies for Pedestrians and Bicyclists addresses the multimodal signal timing for nonmotorized users.
· NCHRP Research Report 959: Diverging Diamond Interchange Information Guide, second edition, presents a comprehensive guide to the design and operation of diverging diamond interchanges (DDI).
· NCHRP Project 03-136, “Evaluating the Performance of Right-Turn-On-Red Operation at Signalized Intersections” addresses performance of right-turn-on-red operations.
· Traffic Signal Management Plan Guidance Document (FHWA-HOP-15-038).
· Traffic Signal Management and Capability Maturity Framework (CMF, FHWA-HOP-16-028).
· Promotion of basic service model concept (FHWA-HOP-09-055) highlighting the need to scale equipment and operations based on agency staff.
Major industry references and standards have been updated with new computational methods and operational practices incorporated.
· Highway Capacity Manual, sixth edition, (HCM6-2016) provides updated procedures for computing the capacity of various highway facilities including signalized intersections.
· NEMA-TS2-2016 Standard incorporates FYA feature, as well as associated configuration and other related information.
· NTCIP 1202 v03A-2019 has updated clauses on FYA and other corrections related to signal operations.
New technological trends are emerging, such as applying new computational approaches to the signal timing process, developing signal timing plans using novel datasets, and implementing new signal timing paradigms for connected and autonomous vehicles (CAV) and connected intersections. The traffic signal timing community has highlighted important topics to be addressed in a new version of the STM, including the signal timing of unconventional intersection geometries; advanced bicycle, pedestrian, and transit signal timing; cybersecurity risks tied to the signal timing procedures; and innovative signal timing design using standards-based controller features.
The STM has served as a primary reference for the FHWA Traffic Signal Timing Concepts course. The course presents a signal timing workflow that starts with goals, explores context with a focus on vehicle flow, and then selects strategies and tactics that support attainment of objectives. It is envisioned that an update to the STM’s structure could better support this workflow, inclusive of performance measurement to validate objectives and demonstrate progress towards goals and enhance the coverage of pedestrians, bicycles, transit, Complete Streets, safety, and equity. The update should consider how signal timing fits in with the overall traffic signal program, as other elements within the program (e.g., maintenance, equipment health) may directly impact the success of signal timing activities.
The objective of this research is to provide guidance on utilizing up-to-date effective practices and research outcomes that have been successfully implemented after STMv2. At the minimum, the research shall:
- Support an objectives-oriented, actively managed traffic signal timing process that starts with goals, considers context, supports the implementation of strategies and tactics, and addresses evaluation of signal timing design outcomes,
- Address signal timing strategies for various intersection and roadway network users, including nonmotorized users and transit vehicles,
- Incorporate existing research and effective practices to expand the coverage of over-saturated/congested conditions, and
- Describe use cases for advanced/innovative controller features, such as peer-to-peer communication, custom logic, etc.
Accomplishment of the project objective will require completion of the following tasks, at a minimum.
PHASE I – Planning
Task 1. Review the pertinent literature on traffic signal timing policies, practices, and techniques; the latest industry standards; and the safety and operational impacts of signal timing decisions. Identify ongoing, relevant research projects and obtain any interim materials, if available. Identify any needed coordination with other ongoing research projects.
Task 2. Develop and employ methods to gain the input of a representative group of practitioners that have firsthand knowledge of the use and application of the STM to gain insights on gaps, and opportunities to improve the content, structure, and range of topics covered in the proposed update.
Task 3 Submit a white paper identifying topics in STMv2 that the research results may influence and new topics for the next update of the STMv2. In addition to those developed through Tasks 1 and 2, it is expected the following topics, at a minimum, will be considered:
· Signal phasing and overlaps
· Multimodal users
· Signal timing strategies for oversaturated conditions
· Interchanges, ramp terminals
· Unconventional intersection geometries
· Priority and preemption
· Automated Traffic Signal Performance Measures (ATSPM) and other performance management approaches
· Custom logic
· Signal timing strategies associated with highway traffic signals that are not traffic control signals (e.g., lane control signals, pedestrian hybrid beacons, ramp meters)
The white paper should assess the maturity and supporting reference material for all proposed topics. For topics not deemed mature, the contractor should discuss research gaps and recommend a strategic approach for addressing these items that includes identifying organizations that might champion these items and advance them to maturity. Discuss the white paper with the project panel in a conference call and finalize a list of topics that have sufficient content for consideration and further development in this project.
Task 4. Prepare Interim Report No. 1 that includes an approach to develop the report addressing the areas approved by the panel in Task 3, and an annotated outline of the manual. The approach should identify appropriate format(s) for the next update of the STMv2 that can accommodate various ways the manual is used and can be made available to users in a sustained manner. The approach must also describe the methodology and rationale for the work proposed for Phase II.
PHASE II – Execution
Task 5. Based on the approved Interim Report No. I, prepare draft language for consideration by FHWA to incorporate the research results in the next update of the STMv2 (herein called FHWA Deliverable) and update all relevant references. The FHWA Deliverable should address all stated project objectives and cover all topics identified through Task 3. The FHWA Deliverable should continue to (1) provide material instrumental to agencies for their own signal timing policies and practices, (2) facilitate the training of new staff, (3) facilitate implementation of more advanced signal timing concepts where appropriate, (4) include examples that illustrate application of the manual material to real-world intersections and roadway networks, (5) include references that promote a deeper understanding of topics, and (6) utilize graphics to help illustrate concepts.
Task 6. Submit a plan for media and communication material to be developed for the project panel’s approval. At a minimum, media and communication materials should include a series of concise videos that demonstrate practitioner uses of the material in the FHWA Deliverable, a two-page executive level flyer describing the practice of signal timing and its benefits, and a syllabus and "train the trainer" materials in PowerPoint format with speaker notes for agencies to incorporate into their training programs.
Task 7. Prepare and submit a revised draft FHWA Deliverable based on the project panel’s review comments.
Task 8. Present the research findings to appropriate American Association of State Highway and Transportation Officials (AASHTO) technical committees for comments and propose any revisions to NCHRP. The research team should anticipate making two presentations during the research to appropriate technical committees at annual meetings of the AASHTO Committee on Traffic Engineering and Committee on Transportation System Operations. Revise the draft FHWA Deliverable after consideration of review comments.
Task 9. Prepare the final deliverables including the following:
1. A conduct of research report that documents the entire research effort, any lessons learned, and a list of potential future enhancements to STM;
2. The proposed FHWA Deliverable;
3. Media and communication materials as approved in Task 6; and
4. A stand-alone technical memorandum titled “Implementation of Research Findings and Products.” See Special Note I for additional information. Additional funding may be available for a follow-up contract on the implementation of the results.
STATUS: A research contractor has been selected for the project. The contracting process is underway.