Two methods of dilemma-zone protection were compared. One was a conventional design with advance detectors at multiple locations. The other was a new design with advance detection at only one location and advance warning flashers on signs, with the legend "Prepare to Stop when Flashing," which are interconnected to the traffic signal. The flashers are activated at a predetermined time before the onset of yellow. Field studies indicated that the performance of both designs depended on the probability that vehicle speeds are in the speed range of their dilemma-zone protection when the green terminated by gap-out. The primary advantage of the new design was its shorter maximum allowable headway, which greatly reduced the probability of max-out and loss of dilemma-zone protection at higher volumes. However, this advantage is diminished at low volumes by the limited speed range for which it provides dilemma-zone protection. The new design was modified to reduce the effects of this limitation and improve the level of dilemma-zone protection it provides.
Abstract