Study Details

Study Title: Superstreet Benefits and Capacities

Authors: Hummer et al.

Publication Date:DEC, 2010

Abstract: This research evaluated operational, safety, and perceived effects of superstreets, called restricted crossing U-turn intersections by FHWA, and developed a useful level of service estimation program which could be used on North Carolina's urban and rural arterial roadway system. The operational analysis involved calibrating and validating VISSIM models of three existing signalized superstreets in North Carolina - two isolated intersections, and one five-intersection superstreet corridor. Results from the three models were compared to results from models of equivalent conventional intersections at various volume levels using travel time as the main measure of effectiveness. The superstreet outperformed the conventional intersection at each location studied, reducing the overall average travel time per vehicle traveling through the intersection. The safety analysis involved three separate methods - naive, comparison-group, and Empirical Bayes. Only unsignalized superstreets were analyzed using the Empirical Bayes method. Three signalized superstreets were also evaluated using SSAM. The results from the analyses were inconclusive with signalized superstreets. Unsignalized superstreets, however, showed a significant reduction in total, angle and right turn, and left turn collisions in all analyses. Analyses also showed a significant reduction in fatal and injury collisions as well. Resident, commuter, and business perceptions of superstreets were evaluated using survey data. The perceptions were mixed within each of the three groups, with some positive and some negative feelings. A LOS program was developed to provide highway capacity and service volumes for superstreets for use in planning applications. The research outcomes will enable NCDOT to have a better understanding of superstreet performance, which can lead to cost saving by reductions in collisions and travel time.

Study Citation: Hummer, J. E., Haley, R. L., Ott, S. E., Foyle, R. S., and Cunningham, C. M. "Superstreet Benefits and Capacities." Report No. FHWA/NC/2009-06, North Carolina State University, Raleigh, NC., (2010). Results also published in: Ott, S. E., Haley, R. L., Hummer, J. E., Foyle, R. S., and Cunningham, C. M. "Safety effects of unsignalized superstreets in North Carolina." Accident Analysis and Prevention, Volume 45, (2012).

Study Report: Download the Study Report Document

CMFs Associated With This Study

Category: Intersection geometry

Countermeasure: Convert a conventional unsignalized intersection to an unsignalized superstreet

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.9912 StarsRear endAllPrincipal Arterial OtherRural
0.87132 StarsSideswipeAllPrincipal Arterial OtherRural
0.41593 StarsLeft turnAllPrincipal Arterial OtherRural
0.85152 StarsOtherAllPrincipal Arterial OtherRural
0.54463 StarsAllAllPrincipal Arterial OtherRural
0.37633 StarsAllK,A,B,CPrincipal Arterial OtherRural
0.25753 StarsAngle,Right turnAllPrincipal Arterial OtherRural