2+1 Roadway Design Guidance Update

Passing slow-moving vehicles on a two-lane highway can frustrate and endanger motorists. To reduce crash rates and improve travel times of Kentucky’s rural two-lane highways, on some routes Kentucky Transportation Cabinet (KYTC) has adopted the use of a 2+1 road design. Typically, a 2+1 design maintains a continuous three-lane cross section, with the center lane used as a passing lane in alternating directions along the highway. 2+1 designs can address operational deficiencies on rural, two-lane highways whose traffic volumes do not warrant a four-lane facility. Compared to two-lane highways, 2+1 roads have better operational efficiency and lower crash rates. They are also significantly less expensive to build than four-lane divided highways (with savings of 50 to 90 percent). KYTC’s Division of Highway Design released design guidance for 2+1 roads in August 2013. Kentucky Transportation Center (KTC) researchers helped develop this guidance. Since then, KYTC has implemented the 2+1 design along several miles of highway, with more scheduled for construction. KTC researchers have participated in the design of these projects and monitored their operations after they were opened to traffic. This research will document current best practices for 2+1 designs, focusing on guidance from KYTC and other state transportation agencies (STAs). One product will be to update the 2013 guidance to reflect best practices from other states and KYTC.


    • English


    • Status: Completed
    • Funding: $85000
    • Contract Numbers:

      KYSPR 21-605

    • Sponsor Organizations:

      Kentucky Transportation Cabinet

      200 Mero Street
      Frankfort, KY  United States  40622
    • Performing Organizations:

      University of Kentucky, Lexington

      Kentucky Transportation Center College of Engineering, 176 Raymond Building
      Lexington, KY  United States  40506-0281
    • Principal Investigators:

      Jasper, Jeff

    • Start Date: 20200200
    • Expected Completion Date: 20200210
    • Actual Completion Date: 0

    Subject/Index Terms

    Filing Info

    • Accession Number: 01751319
    • Record Type: Research project
    • Source Agency: University of Kentucky, Lexington
    • Contract Numbers: KYSPR 21-605
    • Files: RIP, STATEDOT
    • Created Date: Sep 3 2020 2:47PM