Evaluation of NDOR's actuated advance warning systems.

PDFTech ReportNTC report TSPT1-03Dilemma zoneAdvanced driver information systemsDriver support systemsAutomated highway systemsTraffic safetyNebraskaNebraska Transportation CenterAppiah, JusticeWu, ZifengRilett, Laurence R.Nebraska Transportation CenterNebraska. Dept. of RoadsUS Transportation Collection"Driver behavior within the dilemma zone can be a major safety concern at high-speed signalized intersections. TheNebraska Department of Roads (NDOR) has developed and implemented an actuated advance warning (AAW) dilemmazone protection system. Although these systems have received positive reviews from the public\u2014and commercial vehicleoperators in particular\u2014there has been no comprehensive analysis of their effects on safety and traffic operations. Thefocus of this research was to conduct a quantitative study to ascertain the efficacy of the NDOR advance warning system.First, crash records from before and after the implementation of the system at 26 intersections were compared. In addition,29 control intersections were used to compare crash rates over time, and a fully Bayesian technique was employed toensure that no exogenous variables affected the study. Results of the safety analysis were promising (a 43.6% reduction inright-angle crashes) and suggested that the use of the system should be encouraged as an effective safety treatment for thedilemma zone problem at high-speed signalized intersections. Second, a non-intrusive data collection system was used tomonitor traffic and to collect a continuous stream of data up to 1,000 ft upstream of the stop line at two high-speedsignalized intersections equipped with the system. The results suggested that the system was effective at alerting drivers tothe impending end of the green signal: approximately 78% of drivers observed in this study either maintained their speedsor slowed down when the signs began to flash. It was also found that the number of vehicles in their dilemma zones whenthe signal indication changed from green to amber was 77.2% smaller than the number that would have been expected ifthe NDOR AAW system had not been installed. Finally, a modeling framework was developed that could be used toperform consistent, detailed analyses of these systems. Results from two demonstration studies indicated that the proposedprocedure had potential for studying these systems in a microsimulation environment.