Effect of speed/red-light cameras and traffic signal countdown timers on dilemma zone determination at pre-timed signalized intersections.

In this study, the dilemma zone types and lengths were studied according to their definitions based on Gazis, Herman, and Maradudin (GMH) and the probability-of-stopping models, and the link of the two models to each other was explored. Moreover, the effects of the joint and separate use of the speed/red-light camera (SRLC) and the traffic signal countdown timer (TSCT) on dilemma zone determination and safety were investigated. Multiple linear regression was conducted to define the minimum stopping and maximum passing distance boundaries, and binary logistic regression was conducted to define the boundary of dilemma zone type II based on the probability of stopping. The results show that SRLC significantly shifts the dilemma zone downstream and increases the probability of stopping by 11 %. TSCT was found not to have any significant effect on the dilemma zone, but it was found to increase the approaching speeds. It was also found that dilemma zone type II can capture all the dilemma zone types to a great extent.