Safety Effects of Raising Speed Limits to 75 mph and Higher

Over the past decade, there has been a trend toward higher speed limits, especially on rural interstates/freeways. Twelve states have increased speed limits to 75 mph, some as high as 85 mph on freeways and 75 mph on other roads. A number of states have increased speed limits up to 65 to 70 mph on 2-lane rural roads. In some cases these higher posted speed limits exceed design speeds. The impacts of these recent speed limit increases on safety have not been thoroughly studied. There are concerns about increased crash severity resulting from higher speeds. For example, roadside hardware is tested at lower speeds under AASHTO MASH standards, and it is not well understood how various devices may perform on roadways with higher speed limits. Impact performance of a highway feature cannot be measured by a series of crash tests only; even the most carefully researched device has performance limits dictated by physical laws, vehicle stability, and crashworthiness.   The objective of this research is to provide guidance to assist highway agencies in estimating the safety impacts of increasing speed limits to 75 mph or more. This should include information to support the consideration of where, when, and by how much speed limits may or may not be increased on existing facilities and newly constructed roads. The guidance should also identify mitigation strategies that may be implemented to offset potential impacts.  


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  • Status: Completed
  • Funding: $500000
  • Contract Numbers:

    Project 17-79

  • Sponsor Organizations:

    American Association of State Highway & Transportation Officials (AASHTO)

    444 North Capitol Street, NW, Suite 225
    Washington, DC  United States  20001

    National Cooperative Highway Research Program

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

    Jared, David

  • Performing Organizations:

    Texas A&M Transportation Institute, College Station

    Texas A&M University System
    3135 TAMU
    College Station, TX  United States  77843-3135
  • Principal Investigators:

    Dixon, Karen

  • Start Date: 20160919
  • Expected Completion Date: 20220228
  • Actual Completion Date: 20220228
  • Source Data: RiP Project 40219

Subject/Index Terms

Filing Info

  • Accession Number: 01572381
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 17-79
  • Files: TRB, RIP
  • Created Date: Aug 7 2015 1:01AM