Development of a vehicle-following model (VEHFOL) and a heterogeneous traffic simulation model (HETSIM) for controlled intersections

A vehicle-following model, VEHFOL, is developed to represent the flow of heterogeneous or mixed flow traffic. This vehicle-following model is implemented in a comprehensive simulation model, HETSIM, which represents the flow at controlled intersections in India.; VEHFOL considers the longer term goal of a following vehicle achieving a steady state with the lead vehicle. The steady state is characterized by a minimum time gap and equal velocity of the lead and following vehicles. The reaction time of drivers is considered explicitly. A new non-collision constraint that ensures a safe gap from a lead vehicle is formulated. Additionally, a perception threshold heuristic ensures that following vehicles decelerate at an acceptable rate. VEHFOL is validated by comparing model estimates of headway, velocity and acceleration at every simulation time step (0.5 seconds) with observed data. A total of 31 vehicle-following cases, with different combinations of lead and following vehicle types, and modes of operation (accelerating, decelerating, flow during green) are considered. VEHFOL is shown to perform better than two other vehicle-following models implemented in heterogeneous traffic simulation models.; The comprehensive model for simulating heterogeneous traffic through controlled intersections, HETSIM, includes ten vehicle types (seven motorized and three non-motorized). Video data are reduced and used to model the stochastic variation of driver-vehicle characteristics such as acceleration and deceleration rates, and stopped and moving longitudinal and lateral gaps. The unique aspects of lateral movement of heterogeneous traffic, which typically does not travel in lanes, are considered. The four primary vehicle movement sub-models included in HETSIM are: (a) vehicle generation and introduction; (b) overtaking; (c) response to turn intention and (d) response to intersection control.; HETSIM is validated for a wide range of traffic and roadway conditions observed at six intersection approaches, in two cities in India. The primary measures of effectiveness considered are queue length and stopped delay. The application of HETSIM, in studying changes to a traffic network and for developing relationships, is demonstrated. HETSIM may prove too be useful in analyzing the rapidly occurring changes in urban transportation networks in India, and with few modifications, in other countries also.