Rural expressway intersection safety treatment evaluations

A rural expressway is a high-speed, multi-lane, divided highway with partial access control which may consist of both at-grade intersections and grade separated interchanges. Many State Transportation Agencies (STAs) are converting rural two-lane undivided highways into expressways for improved safety and mobility; however, collisions at two-way stop-controlled (TWSC) intersections (particularly far-side right-angle crashes) on rural expressways are reducing the safety benefits that should be achieved through conversion. When the safety performance of these intersections begins to deteriorate, the improvement path typically begins with the application of several signing, marking, or lighting improvements, followed by signalization, and ultimately grade separation. Because signals hamper the mobility expressways are meant to provide and because interchanges are not economically feasible at all problematic intersections, there is a need for more design options at TWSC rural expressway intersections. Some STAs have experimented with innovative rural expressway intersection safety treatments to avoid signalization and grade separation; however, little is known about the safety effects of these designs. Therefore, the objective of this research was to document their experience with these treatments and to conduct nayve before-after safety evaluations where possible. The ten case studies included within this thesis investigate J-turn intersections, offset T-intersections, jughandle intersections, Intersection Decision Support (IDS) technology, static roadside markers, left-turn median acceleration lanes (MALs), offset right-turn lanes, offset left-turn lanes, enhanced intersection guide signing, and dynamic advance intersection warning systems. These case studies help to begin to understand the safety improvement potential of these countermeasures and start to set the stage for the development of a richer set of design options at TWSC rural expressway intersections