Rural Expressway Intersection Design Guidance

A rural expressway is a high-speed, multilane, divided highway with partial access control with both at-grade intersections and grade-separated interchanges. Many state transportation agencies are converting rural two-lane undivided highways into expressways for improved safety and mobility. However, collisions at two-way stop-controlled (TWSC) expressway intersections are reducing the safety benefits that should be achieved after conversion. When the safety performance of these intersections deteriorates, the countermeasure path typically begins with several signing, marking, or lighting improvements, followed by signal-ization, and could ultimately result in grade separation. Signals are not always effective at improving safety and hamper the mobility expressways are meant to provide. Interchanges are not economically feasible at every problematic intersection and can take years to develop; therefore, more design options at TWSC rural expressway intersections are needed. Some state transportation agencies have experienced success with innovative rural expressway intersection countermeasures that are not currently included as design options within national guides. Therefore, NCHRP Report 650: Median Intersection Design for Rural High-Speed Divided Highways, was commissioned to recommend revisions to AASHTO's A Policy on Geometric Design of Highways and Streets (Green Book) and the Manual on Uniform Traffic Control Devices (MUTCD) regarding rural expressway intersection design. Project tasks included summarizing existing expressway intersection design guidance within these national guides, documenting state transportation agency experience with innovative rural expressway intersection safety treatments, and recommending revisions to the Green Book and the MUTCD.