A review of the yellow interval dilemma

Abstract

This paper deals with the evolution of rules concerning the setting of the yellow interval duration of a traffic light and the associated “amber (yellow) light dilemma”. By employing realistic estimates of dynamical characteristics of vehicles, we investigate all possible options available to a driver facing a yellow signal. We show that the dilemma may be eliminated if the yellow interval duration is set according to a formula given by Gazis, Herman and Maradudin (GHM), for a given intersection geometry and an approach speed equal to the speed limit. We also show that a driver traveling with a speed less than the speed limit and being within his own dilemma zone from an intersection when the yellow indication commences, as defined by GHM, is able to clear the intersection if the yellow duration is set according to the formula given by GHM using the speed limit, but only by accelerating toward a speed equal to or higher than the speed limit. We comment on the redundant formulation of partitioning a yellow interval into a ‘yellow’ and a ‘red clearance’ interval. Finally, we present a brief historical review of the investigations and practices regarding the setting of the yellow (amber) interval duration, and conclude with recommendations concerning the setting and associated traffic ordinances.