Mid-America Transportation Center


Date of this Version


Document Type



Report # MATC-UNL: 221 Final Report 25-1121-0001-221


Copyright 2012 Mid-America Transportation Center


Each day, millions of signal changes to the yellow phase occur at isolated high speed intersections, when erroneous driver decisions to stop or go may often lead to a crash. Dilemma zone protection systems are typically used to control these intersections in order to ensure the safe and efficient movement of vehicles. However, traditional dilemma zone protection systems show deterioration in performance during medium to heavy traffic volume conditions, jeopardizing both the safety and efficiency of intersections. The performance of these control systems for heavy vehicles is even more greatly affected, as traditional dilemma zone boundaries were developed for passenger vehicles. Research conducted by the authors found that to have the same level of protection as passenger vehicles, heavy vehicles needed to be protected for twice as long. The traditional surrogate measure of safety, the dilemma zone, marks the region of risk at high speed intersections, but does not quantify the level of risk, which is essential from an economic framework. In the current study, an improved surrogate measure of safety, the dilemma hazard function, was developed by expanding the existing measure of safety, utilizing the concept of traffic conflict. The probability of traffic conflict defined the dilemma hazard function, which was used to quantify safety benefits for high speed intersections. A behavioral model was used to develop the dilemma hazard function for passenger vehicles and heavy vehicles using data collected at a typical high speed intersection site in Noblesville, Indiana. The advent of advanced wide area detector technology made it feasible to assume that the dilemma hazard function could be developed for each site, hence, barring the need for a search for a universal dilemma hazard function.