Dedicated right-turn lanes (RTLs) typically are installed on highways and arterial roads at intersections to improve motor vehicle traffic operations and avoid high-speed rear-end crashes. However, vehicles decelerating or queued in an RTL may obstruct the view of drivers turning onto or crossing the major road from the minor road at stop-controlled intersections where operating speeds are relatively high on the major road. Additionally, weaving maneuvers among bicyclists and right-turning motor vehicles may present added conflicts.
Some studies indicate that drivers may not perform as expected at parallel-type RTLs. Some studies suggest that tapered-type RTLs or offsets with more separation may maintain the sight triangle and improve safety performance. In any case, empirical safety data indicate that crash frequency for drivers making entering or crossing movements from the minor street may increase at RTLs, and there is little guidance available for designers of these turn lanes. Research is needed to assess the safety performance of RTLs; identify design characteristics—for example offsets, signage and striping, storage length, and taper—that influence safety performance; and provide guidance for designers.
The objective of this research is to develop recommendations for design of RTLs on rural and suburban roads to enhance safety performance. These recommendations and supporting information should be consistent with the AASHTO Highway Safety Manual (HSM) and suitable for adoption in state and local highway design guides and possibly the AASHTO Policy on Geometric Design for Highways and Streets.
Interim Deliverables will include:
Interim Report 1 (IR1) presenting a critical review of safety performance of a representative selection of RTLs on rural and suburban roads, with particular emphasis on stop-controlled intersections.
Interim Report 2 (IR2) presenting an analysis of three-dimensional sight-line characteristics and driver actions at representative intersections on rural and suburban roads with RTLs.
Interim Report 3 (IR3) presenting guidance and recommendations for design of intersections on rural and suburban roads with RTLs to improve safety performance for all road users.
Draft final report comprising (a) recommendations for RTL design on rural and suburban roads and (b) documentation of the research underlying the recommendations.
STATUS: The project is active.