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https://www.nationalacademies.org/trb/events

Impacts of Turn Lanes on Speed and Crashes Involving Vulnerable Road Users in Urban Areas

Turn lanes, one of the Federal Highway Administration’s (FHWA’s) proven safety countermeasures for motor vehicles, are recommended to reduce the risk of collisions involving vehicles turning left across opposing through traffic and rear-end collisions. However, a preliminary analysis of 2017–2024 crash data from Washington State indicated that pedestrian-involved fatal and serious injury crashes occurred more frequently at intersections with left turn lanes, and at intersections with both right and left turn lanes, compared to intersections with no turn lanes. This raises important questions about how turn lanes influence intersection safety for all road users: (1) What effect do turn lanes have on operating speeds at the intersection and along the broader corridor? (2) How do turn lanes impact the risk of fatal and serious injury crashes for vulnerable road users (VRUs)? While turn lanes may improve network efficiency and reduce vehicle conflicts, they may diminish a traffic calming feature that has a wider effect on vehicle operating speeds. Turn lanes also may influence VRUs’ conspicuity and predictability, increasing crossing distances, and creating additional vehicle–VRU conflict points through altered temporal and spatial separation between modes. Research is needed to quantify these effects, evaluate turn lanes (including their effects on crash exposure, likelihood, and severity), and provide actionable recommendations. OBJECTIVE: The objective of this research is to quantify impacts of turn lanes on vehicle operating speeds and VRU fatal and serious injury crashes in urban areas. The research shall focus on the following aspects: (1) Evaluate impacts of the presence of turn lanes on: operating speeds of turning vehicles at conflict points with VRUs; operating speeds of vehicles along corridors; and approach speeds of through vehicles adjacent to turn lanes. (2) Investigate correlations between turn lanes and VRU fatal and serious injury crashes to develop crash modification factors (CMFs) for removing turn lanes to potentially reduce VRU fatal and serious injury crashes. Accomplishment of the project objective will require at least the following tasks. TASKS: Task descriptions are intended to provide a framework for conducting the research. The NCHRP is seeking the insights of proposers on how best to achieve the research objective. Proposers are expected to describe research plans that can realistically be accomplished within the constraints of available funds and subaward time. Proposals must present the proposers' current thinking in sufficient detail to demonstrate their understanding of the issues and the soundness of their approach to meeting the research objective. The research shall focus on urban areas with posted speed limit of 45 mph or less. Proposers may also recommend and justify additional or alternative criteria based on their understanding of the research needs. PHASE I – PLANNING: (Task 1) Conduct a comprehensive literature review of research. The review shall include state and local agencies; the American Association of State Highway and Transportation Officials (AASHTO), the National Association of City Transportation Officials (NACTO), and the Institute of Transportation Engineers (ITE) guidelines and standards; and published and unpublished research conducted through the NCHRP, FHWA, and other national, international, state, and pooled fund sponsored research. High-level policy documents should be considered for this task as appropriate. Synthesize findings from the literature review with a focus on how turn lanes affect operating speeds, and fatal and serious injury crashes involving VRUs in urban context. Incorporate documented before-and-after crash evaluations involving turn lane removal or repurposing for traffic calming treatments. (Task 2) Propose research methodology to achieve the research objective (see Special Note A). This methodology will be fully developed in Phase II and shall, at a minimum, include the following components: (1) For the first aspect of the objective: (a) Elements, criteria, and scenarios to be considered and prioritized in the research; (b) A comprehensive data collection plan; and (c) A plan for assessing the impact of turn lanes on operating speeds for turning vehicles, through vehicles, and along the corridor. (2) For the second aspect of the objective: (a) A revised and expanded data collection plan that builds on the first aspect and focuses on historical crash data; (b) An approach for comparing test sites and comparison sites, with and without turn lanes; (c) A plan for assessing the impact of turn lanes on fatal and serious injury crashes for VRUs; and (d) A plan to develop CMFs with a three-star or higher rating (for left-turn lanes only, right-turn lanes only, and/or combined). (Task 3) Prepare an annotated outline for the research report. (Task 4) Prepare Interim Report No.1 documenting the results of Tasks 1 through 3 and provide an updated plan for the remainder of the research no later than 4 months after subaward. The updated plan must describe the process and rationale for the work proposed for Phases II. Note: Following a 1-month review of Interim Report No. 1 by the NCHRP, the research team will be required to meet with the NCHRP project panel in-person in Washington, DC to discuss the interim report. Work on Phase II of the project will not begin until authorized by the NCHRP. Phase I budget shall not exceed $50,000. PHASE II — EXECUTION AND FINAL DELIVERABLES: (Task 5) Execute the methodologies outlined in Task 2 in accordance with the approved Interim Report No. 1. Provide monthly data collection updates to NCHRP, and document the effects of turn lanes on speed and the development of CMFs that meet three-star or higher criteria. (Task 6) Develop and submit a draft research report and document(s) that support the CMFs to be considered by the CMF Clearinghouse. (Task 7) Conduct two in-person presentations of the panel-approved research results to two appropriate AASHTO committees, such as the Technical Committee on Non-motorized Transportation and Subcommittee on Local Road Safety, for comments; propose any revisions to the NCHRP panel. Finalize the draft research report after consideration of practitioners' feedback. (Task 8) Develop a draft PowerPoint presentation with speaker notes summarizing the revised research report. The presentation slides shall specify the research objective, key findings, research products developed, and benefit or value of the research findings. (Task 9) Prepare the final deliverables, including: (1) A final research report documenting the entire research process and findings; (2) Document(s) that support the CMFs to be considered by the CMF Clearinghouse; (3) A final PowerPoint presentation with speaker notes summarizing the revised research report; and (4) A technical memorandum titled “Implementation of Research Findings and Products” (see Special Note K). Note: The research plan may include additional deliverables and panel meetings via teleconferences. Note: Following receipt of the draft final deliverables, the remaining 3 months shall be for NCHRP review and comment and for research agency preparation of the final deliverables.

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  • English

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Filing Info

  • Accession Number: 01956612
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 17-145
  • Files: TRB, RIP
  • Created Date: May 28 2025 2:15PM