Assessing the Impacts of Turn Lanes in Different Contexts and Modal Considerations to Increase Safety Performance

Developing a better understanding of the role a turn lane has on reducing crashes is becoming increasingly important as small changes to the roadway can result in significant costs to agencies. Current design and operational philosophies are commonly focused on whether a lane is needed and how will the installation of that lane affect operations; however, limited understanding exists regarding key factors in the safety decision making process to quantifying the turn lane safety performance characteristics (such as length of storage, deceleration length area, taper treatment, offset, etc.). For some locations, the turn-lane crash modification factors are quite significant, and at other locations and contexts, the factors are quite low. While much research exists on turn lanes, both from a safety and operational perspective, data is typically aggregated in a manner that does not allow for the fine tuning of safety considerations. The intent of this research would be to understand the impacts of turn lane design on the safety of a facility, given different modal priorities, context, and traffic mix (e.g., freight, pedestrians, and bicyclists) under different levels of traffic. Consideration of left and right turns is often a benefit to the vehicle but a disadvantage to the bicyclist and pedestrian because of in-creased exposure, speeds, and crossing distances. The safety aspects of turn lane design and location should consider the implications of the “do nothing” option. As an example, left turn lanes at rural four-lane highways may only be constructed if the turning volume exceeds a minimum threshold, yet the absence of the turn lane for even one or two vehicles may result in severe rear-end, angle, or sideswipe crashes at isolated locations. Alternative turn lane design options, such as constructing a short turn lane so as to provide limited storage, can be expected to directly influence safety performance at these locations. There is a need to take a microscopic view of design and operations of turn lanes and their impacts on safety to both vehicles and other vulnerable road users to evaluate the safety performance of various designs on differing facilities, modal mixes, and contexts to better allow for categorization of new design approaches. Research is needed to develop a better understanding of the current basis for the design of turn lanes at intersections and provide updated criteria to enhance design and operational performance of future designs based on the data-driven analysis. The objective of this research is to describe key parameters and decision criteria to enhance the safety of turn lanes and provide safety models and crash modification factors that practitioners can use to evaluate design and operational treatments for turn lane safety. Achieving this objective may entail the following tasks: (a) review of literature and current practice regarding treatment of design and operational considerations for turn lanes in multiple contexts and traffic characteristics, (b) identification of key parameters and decision criteria to be considered in turn-lane provision, (c) development of safety models for evaluating turn lane impacts on safety for all modes, (d) development of crash modification factors for applications involving turn lanes, and (e) preparation of a guidebook or materials to supplement the Highway Safety Manual presenting the models and crash modification factors in a manner to facilitate practitioner usage.


  • English


  • Status: Proposed
  • Funding: $650000
  • Contract Numbers:

    Project 07-28

  • Sponsor Organizations:

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590

    American Association of State Highway and Transportation Officials (AASHTO)

    444 North Capitol Street, NW
    Washington, DC  United States  20001
  • Project Managers:

    Lemer, Andrew

  • Start Date: 20180618
  • Expected Completion Date: 0
  • Actual Completion Date: 0

Subject/Index Terms

Filing Info

  • Accession Number: 01672241
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 07-28
  • Files: TRB, RiP
  • Created Date: Jun 18 2018 3:02PM