Traffic Flow Analysis at Manual Tollbooth Operation under Mixed Traffic Conditions

Abstract

Heterogeneous traffic conditions prevail in all countries across the world, but the degree of heterogeneity is different in developed and developing countries. In the United States, heavy vehicles (trucks and buses) are mixed with passenger cars, whereas more than seven different categories of vehicles in India are observed in the traffic stream. Such heterogeneity is also observed at tollbooths, where dedicated lanes are provided for each vehicle category; however, during peak hours, lane discipline is broken, and the same lane is used by different categories of vehicles. Such mixed traffic conditions lead to wide variations in service time for the same vehicle category and, hence, reduce tollbooth capacity. To convert the mixed traffic flow into the equivalent passenger car, the tollbooth equivalency factor (TEF) is proposed in the present study. The TEF is based on the service time and clearance time of a vehicle with respect to a passenger car at the same tollbooth. The TEF is found not to be a fixed value but varies with the approaching mixed traffic volume and composition of traffic in the queue. Vehicles in the traffic stream are divided into seven categories, and simultaneous equations are developed to determine the service time of a vehicle type based on approach volume and traffic composition. These equations are further used to depict variations in TEF with varying approach volume and composition. The change in TEF values is explained on the basis of the relative change in service time of a vehicle type with respect to a standard car at different volume levels. The accuracy of the TEF values estimated through simultaneous equations is checked by comparing the estimated values with those calculated directly from the field data. TEF values obtained for each type of vehicle are multiplied by the number of that vehicle type to obtain the approaching mixed traffic volume in an equivalent homogenous mix (TEF/h). This method will naturally require an estimation of TEF for each vehicle type from the field data. To avoid this exercise, the stream equivalency factor (SEF) at the tollbooth is proposed, which provides an overall multiplying factor for the entire traffic volume to convert heterogeneous traffic into the homogenous equivalent. The results presented in this paper will be useful for planners and tollbooth managers for the design and performance evaluation of toll plazas and to identify the number of lanes required during peak and nonpeak hours.