An Update on Superstreet Implementation and Research

Superstreets are promising solutions for arterials. They have the potential to move more vehicles efficiently and safely through the same amount of pavement as conventional arterials, at-grade, with minimal disruptions to the surrounding environment and businesses. A superstreet works by redirecting left turn and through movements from side streets. Instead of allowing those to be made directly through a two-way median opening, as in conventional design, a superstreet sends those movements to a one-way median opening 800 feet or so downstream. Besides safety, capacity, and travel time, another profound change provided by a superstreet is in progression. With a superstreet, the signals that control one direction of the arterial can operate independently from the signals that control the other direction. This means that a superstreet can operate like a pair of one- way streets, and that perfect progression is possible at any speed with any signal spacing. This is an extraordinary capability; conventional arterials cannot approach this efficiency even with excruciating control of accesses and signal installations. The superstreet concept was developed in the early 1980s. Maryland and North Carolina have led the world in superstreet development. The North Carolina Department of Transportation (NCDOT) built its first superstreet in a rural area as a safety countermeasure in 2000. The NCDOT opened its first signalized version in a suburban area in June 2006. The NCDOT has also adopted the superstreet as an appropriate design for important segments of its Strategic Highway Corridor system. Maryland has had “j-turn” intersections in place since the early 2000s. The purpose of this paper is to provide an update on recent work on superstreets. The paper concentrates on safety and reviews the performance of several recent superstreet installations in North Carolina and Maryland. The first superstreets have generally performed well. The rural applications in Maryland, in particular, have led to dramatic safety improvements. A rural superstreet application in NC has resulted in modest safety gains, and a signalized suburban application in NC has resulted in a collision rate below the statewide average for that type of roadway. The paper briefly reviews other experiences with superstreets. In general, agencies looking for alternatives for miserable stretches of arterial will benefit from learning about the experience with superstreets in North Carolina and Maryland.