Derivation of Capacity Standards for Intercity Roads Carrying Heterogeneous Traffic using Computer Simulation

The knowledge of roadway capacity is an important basic input required for planning, analysis and operation of roadway systems. Expressing capacity as number of vehicles passing a given section of road or traffic lane per unit time will be inappropriate when several types of vehicles with widely varying static and dynamic characteristics are comprised in the traffic. The problem of measuring volume of such heterogeneous traffic has been addressed by converting the different types of vehicles into equivalent passenger cars and expressing the volume in terms of Passenger Car Unit (PCU) per hour. The effect of variation of traffic volume, road width, magnitude of upgrade and its length on PCU value is studied. A recently developed heterogeneous traffic-flow simulation model, named, HETEROSIM is used for this study. Field data collected on traffic flow characteristics are used in calibration and validation of the simulation model. The validated simulation model is then used to derive PCU values for different types of vehicles. The PCU estimates, made through microscopic simulation, for the different types of vehicles of heterogeneous traffic, for a wide range of traffic volume and roadway conditions indicate that the PCU value of a vehicle significantly changes with change in traffic volume, width of roadway, magnitude of upgrade and its length. Using the derived PCU values, capacity guidelines are also developed for typical roadway and traffic conditions.