Intersection Safety at High-Speed Signalized Intersections: Number of Vehicles in Dilemma Zone as Potential Measure

High-speed signalized intersections may have both safety and operational problems. The safety problems traditionally have been solved with the use of dilemma zone protection of some form. However, dilemma zone protection tends to be associated with an increasing chance of running the phase to its maximum allowable duration—a max-out. At max-out, any provided dilemma zone protection ceases and any number of vehicles may be in the dilemma zone, a situation that creates the safety problem the system was meant to prevent. Most methods for assessing the safety of intersections do not include an assessment of signal operations. Reducing the number of vehicles in the dilemma zone for an intersection approach should reduce the number of drivers who do not receive dilemma zone protection and thereby reduce the probability of crashes for those approaches. A theoretical method calculates the number of vehicles in the dilemma zone at the end of a green phase, which can then be used to compare real-world and theoretical performance of different detection systems. An illustrative example provides one such comparison. Also, a field data collection method is provided for the assessment of a signal system in operation.