Auxiliary Turn Lane Design Guidance and Policy Upgrades

There are approximately 6 million traffic crashes annually (2006). Fifty-three percent of these occur at intersections (3.1 million crashes). Auxiliary turn lanes have been clearly identified as a significant countermeasure to address these crashes. The draft Highway Safety Manual (HSM) suggests that 64.6 percent of rural intersection crashes are susceptible to remedy by auxiliary lane. i.e. those crashes that involve another vehicle in a maneuver other than a rear-end crash. Additionally, the HSM suggests that 66 percent of urban multilane stop control and 55 percent of fatal and injury intersection crashes are susceptible to remedy by auxiliary lane. Auxiliary turn lanes at intersections generally have a traditional or offset design. The design components of a traditional turn lane consist of the length needed to store an appropriate number of waiting vehicles, a vehicle deceleration area, and the taper needed to develop the full lane width. Offset turn lanes have similar components but they are developed in a manner different from traditional designs. The guidance and practice used throughout United States for traditional and offset turn lane designs and application also vary by intersection location (e.g., rural or urban), traffic control (e.g., stop-control or signal-control), and/or turn lane type (e.g., right- or left-turn). The AASHTO<em> Policy on Geometric</em> <em>Design of Highways and Streets</em> (<em>Green Book)</em> contains criteria for geometric design of auxiliary turn lanes. While acceptable for current practice, the basis for the design and policy elements of these features is recognized as needing more support. There is, therefore, a general need to confirm, update, and/or expand upon the operational and safety assumptions and basis for the design of traditional turn lanes that are in the AASHTO <em>Green Book</em>. The soon-to-be-published HSM includes the overall safety basis for left and right turning lanes at intersections but does not identify crucial aspects of positive offset, angled vs. parallel auxiliary lane design, etc. In addition, it may also be appropriate to propose or update guidance for when and where left- or right-turn lanes are justified from both an operational as well as a safety basis. Finally, similar guidance or policies and detail are needed for offset right- and left-turn lane design. There is a high level of variability in the application of offset turn lanes in the United States. An investigation and proposal of acceleration and deceleration speed change lane design guidance may also be appropriate. It is expected that the results of this research will be used directly in an update to the AASHTO <em>Green Book</em> and therefore be made directly available to practitioners across the country. The objective of the research is to confirm, strengthen, and/or update the current design guidance for turn lanes at both unsignalized and signalized intersections in urban and rural areas.


  • English


  • Status: Proposed
  • Funding: $400000.00
  • Contract Numbers:

    Project 3-102

  • Sponsor Organizations:

    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

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001
  • Project Managers:

    Derr, B

  • Start Date: 20100613
  • Expected Completion Date: 0
  • Actual Completion Date: 0
  • Source Data: RiP Project 26459

Subject/Index Terms

Filing Info

  • Accession Number: 01463928
  • Record Type: Research project
  • Source Agency: National Cooperative Highway Research Program
  • Contract Numbers: Project 3-102
  • Files: TRB, RiP, USDOT
  • Created Date: Jan 3 2013 2:33PM