VEHICULAR INTERACTION AT SIGNALIZED INTERSECTIONS

Abstract

The traffic in most developing countries such as India is heterogeneous, comprising vehicles of wide ranging physical dimensions, weight, and dynamic characteristics, moving on any available part of road space without lane discipline. The unrestricted movement of vehicles makes the lane concept and expression of flow values, based on standard lane width, invalid. In such scenario knowledge of vehicular interaction as the heterogeneous traffic stream discharge from signalized intersection when the signal changes to green is the crucial aspect in determining the capacity of the intersection. The interaction between vehicles of a mixed traffic stream is maximum during discharge of a queue from the intersection when the signal light changes to green. One way of expressing this interaction between the vehicles is by computing their Passenger Car units (PCU). The PCU for a vehicle type depends up on the relative difference in static and dynamic characteristics when compared to cars. Apart from this, the geometric conditions and traffic stream characteristics will also influence PCU factors. Data collected in 1994 at 4 signal controlled intersections are analysed to estimate PCU values of different vehicle groups and to investigate the variation in the PCU values with approach width, turning radius and saturated green. Nine through and six right turn approaches were considered. The vehicles are categorized in to four categories and their PCU's are computed at each intersection. The variation of PCU with saturated green, approach width and turning radius are explained graphically. It is found that the PCU for a vehicle type increases with all these factors. It increases with saturated green because of iii sufficient warm-up time in longer green phases, and it increases with approach width and radius of turn due to more freedom enjoyed by individual vehicles. To investigate changes in vehicular interaction due to the introdUction of small sized new technology car with better acceleration and maneuverability capability, new data collected in 2008 at three signal controlled intersections were analyzed. Six through and five right turn approaches were considered. PCU values of vehicle groups and saturation flow are compared with those found from 1994 data. The result indicated that there is a significant increase in PCU values as well as in the saturation flow. iv