Mid-America Transportation Center


Date of this Version


Document Type



Report TSPT1-03 Final Report 26-1118-0086-001


Copyright 2011 Mid-America Transportation Center


Driver behavior within the dilemma zone can be a major safety concern at high-speed signalized intersections. The Nebraska Department of Roads (NDOR) has developed and implemented an actuated advance warning (AAW) dilemma zone protection system. Although these systems have received positive reviews from the public—and commercial vehicle operators in particular—there has been no comprehensive analysis of their effects on safety and traffic operations. The focus 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 to ensure that no exogenous variables affected the study. Results of the safety analysis were promising (a 43.6% reduction in right-angle crashes) and suggested that the use of the system should be encouraged as an effective safety treatment for the dilemma zone problem at high-speed signalized intersections. Second, a non-intrusive data collection system was used to monitor traffic and to collect a continuous stream of data up to 1,000 ft upstream of the stop line at two high-speed signalized intersections equipped with the system. The results suggested that the system was effective at alerting drivers to the impending end of the green signal: approximately 78% of drivers observed in this study either maintained their speeds or slowed down when the signs began to flash. It was also found that the number of vehicles in their dilemma zones when the signal indication changed from green to amber was 77.2% smaller than the number that would have been expected if the NDOR AAW system had not been installed. Finally, a modeling framework was developed that could be used to perform consistent, detailed analyses of these systems. Results from two demonstration studies indicated that the proposed procedure had potential for studying these systems in a microsimulation environment.