Executive Summary : | Road traffic accidents are one of the leading reasons for human fatalities. With only 2% of the global vehicular volume, Indian road traffic contributes to 11% (highest) of the global road accidents. Hence studies focusing on in-depth road safety-related aspects are pivotal in determining the implications of traffic behaviour and operations on traffic safety. Unlike in developed countries, the urban roads of developing economies like India are characterised by a high degree of heterogeneity and a weak lane discipline. Due to this, vehicular interactions with each other are multi-dimensional and complex in nature. Also, the traffic behaviour of different vehicle classes is significantly different, making the assessment of traffic behaviour and safety aspects for Indian traffic and challenging problem. At signalised intersections, the highest speeds of the vehicles are observed before the end of the green phase and the onset of the red phase, especially at the undersaturated signalised intersections. Before the onset of the red phase, the amber (yellow) phase is provided. The functioning of the red and green phases is clear. However, during the amber phase, the drivers close to the stop-line may cross, and drivers at a significant distance should decelerate and stop to safely arrive at the intersection and avoid red-light violations. Hence, the amber phase also serves as a buffer zone between two conflicting green phases. Apart from the microscopic driving behaviour parameters studied for signalised intersection, the decision to stop or go during the amber phase is a key parameter that significantly influences the traffic behaviour and safety aspects. In many instances, a driver is unable to decide whether to stop or go during the amber phase. This delay or dilemma in decision making often leads to aggressive decelerations to stop or red-light violations that often result in rear-end or side-impact/head-on collision, often of very high severity. Hence the traffic behaviour and consequently the assessment of stop and go decisions by drivers becomes pivotal in assessing the safety aspects and design efficiency of the signalised intersections.
For quantifying the effect of dilemma in decision making on traffic behaviour and safety aspects, robust models for dilemma zone identification are pivotal. The region in the upstream vicinity of the intersection where a dilemma is generally faced is called the dilemma zone. The dilemma zone is dynamic in nature and is observed to be predominantly dependent upon the distance and speed of the vehicle and several other factors. Studies report that the dilemma zone is also equally dependent upon the time remaining for the phase change (amber phase duration). However, studies on dilemma zone in India are limited and restricted to only distance-based dilemma zone identification. Moreover, the models available are limited to a single metropolitan and not tested for their transferability. |