An update of the Green Book Design Vehicles and Minimum Turning Paths

The current design vehicle classifications in AASHTO’s A Policy on Geometric Design of Highways and Streets (Green Book) have been developed over a 40+ year period. These design vehicle dimensions and minimum turning radii, while providing full coverage of the general vehicle fleet, are difficult to support and verify. This difficulty is a result of the limited or nonexistent supporting data and research for these vehicles. Questions have been raised about the steering angles for some of the Green Book design vehicles that appear small for the modern vehicle (e.g., 13 degree steering angle for the WB-92D and WB-109D). This can result in overly conservative or large geometric layouts and striping plans. Further, with the increased usage of modern roundabout designs, accurate vehicle steering angles and swept paths are of utmost importance. The Technical Committee on Geometric Design (TCGD) recently received pre-ballot review comments on the Green Book, 7th Edition, from members of the AASHTO Subcommittee on Design. Several comments were related to the turn radii and prevalence of different design vehicles which can have a major impact on intersection and interchange design. The Green Book turning path templates provide insufficient data for software developers, such as AutoTURN, to incorporate the turning paths in CAD programs without making assumptions such as the kingpin and hitch locations. As such, the CAD programs provide similar but different turning paths than the Green Book templates. Further, with industry movement toward 3D design, ground clearances or heights of the various design vehicles are needed but not provided by the Green Book. The objective of this research is to develop material for the 8th Edition of the Green Book that ensures the design vehicle classes represent the vehicles on the roads, including the elimination of any inconsistent and unrealistic vehicle characteristics. The research should provide guidance on the use, application, or general conservativeness of the templates. The research will provide missing design vehicle information required for 3D design applications.


  • English


  • Status: Proposed
  • Funding: $400000
  • Contract Numbers:

    Project 07-27

  • 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:

    Derr, B

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

Subject/Index Terms

Filing Info

  • Accession Number: 01672240
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 07-27
  • Files: TRB, RiP
  • Created Date: Jun 18 2018 3:02PM