SPR 21-605: 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 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. Through project development and observations of traffic operations, many lessons have been learned since original design guidance was published. OBJECTIVES • Document current best practices for 2+1 designs. This review will focus on guidance from KYTC and other state transportation agencies (STAs). • Interview practitioners from KYTC and other STAs to assess the operation and performance of their 2+1 roads and catalogue lessons learned. • In collaboration with Cabinet staff, update the 2013 guidance to reflect best practices from other states and KYTC.