MINIMISATION OF DILEMMA ZONE AT SIGNALIZED INTERSECTION UNDER MIXED TRAFFIC CONDITIONS

Abstract

Traffic signals are extensively used to control the traffic at road intersections in urban areas. These siL.nals are designed to optimise capacity and safety for the volume of traffic approaching the intersection. The usual signal sequence is red, green and amber. The amber signal alerts the drivers that the red signal is about to commence shortly and the related green aspect is about to be terminated. Improperly designed amber time may create dilemma to the drivers, whether to stop or to continue at the onset of amber. Due.. to this dilemma, accidents as well as risk of rear-end collisions get increased. It has been reported that at a typical site, more than 5000 drivers per year may be caught in the dilemma zone if amber time is not properly designed. Many researchers (Webster, 1959; Gazis, et at., 1960; Olson, et al., 1962) have related amber period with parameters like reaction time of drivers, approach speed of the vehicles, width of intersection, lengths of vehicles etc. based on their studies. In India, the traffic is of mixed nature with varying static (weight, length, width and height) and dynamic (acceleration, deceleration capacity, braking efficiencies and maneuverability) characteristics. Therefore, requirement of amber time will be different for different type of vehicles. In the present study, an attempt has been made to evaluate the effect of mixed traffic on the dilemma zone. Data collected at eight approaches of four signalized intersections in Delhi have been analysed. The driver behaviour at the onset of amber is presented a.., a function of probability of stopping and distance to (ii) the stop line. The variation of dilemma zone with different parameters of mixed traffic has also been investigated. It is observed that the existing amber time at the approaches selected for study is not sufficient for drivers to take the appropriate decision. It is expected that the new amber time designed by minimising the length of dilemma zone will reduce the number of drivers caught in dilemma considerably. (Key words: amber time, dilemma zone, driver behaviour, mixed traffic, signalized intersection).