To stop, or not to stop, that it the dilemma: evaluating the effects of safety countermeasures at signalized intersections during the yellow phase

At the onset of the yellow phase of signalized intersections, the approaching drivers may hesitate to decide to go or stop due to the dilemma zone (DZ). The drivers who decide to pass through the intersection might occur in red light violations and right-angle crashes, while some others might stop suddenly and prematurely with the subsequent risk of rear-end collisions. This study is aimed at analyzing the driver's behavior at the onset of the yellow signal, and identifying the most effective safety countermeasure for the resolution of the dilemma zone in order to help drivers in their stop/go decisions and reduce the risk of crashes. To achieve this objective, a driving simulator study was carried out and the effects of the following countermeasures were tested on a signalized intersection of an urban scenario: i) Green Signal Countdown Timers GSCT (C1); ii) newly developed horizontal marking and vertical warning sign (C2); iii) an in-vehicle advanced driving assistance system based on augmented reality and connected vehicle technologies (C3). The results revealed that the most effective countermeasure was C3 which provided the drivers with prompt and personalized suggestions based on their actual speed; in fact, a major reduction of Red Light Running (RLR) and length of the dilemma zone were recorded. C2 resulted in a significant reduction of the dilemma zone with the greatest consistency in driver decision-making behaviors. Finally, using C1 it was observed an unnecessary increase in early stopping rates with a reduction of the intersection efficiency.