MODELLING OF MIXED TRAFFIC ON A TWO LANE ROAD USING CELLULAR AUTOMATA

Abstract

Traffic simulation is an important aspect of analyzing traffic flow. Several techniques are available for this purpose. Recently researchers have found a new paradigm popularly known as cellular automata (CA). CA consists of an infinite, regular grid of cells, each in one of a finite number of states. The grid can be in any finite number of dimensions. Every cell has the same rule for updating, based on the values in its neighborhood. Out of 256 possible rules for update, rule 184 is used for showing the vehicle movement. An empty cell denotes no vehicle in the cell representing a cell value 0 and a filled cell denotes presence of a single vehicle representing a cell value 1. Cellular automata are extensively used for modeling of traffic on single lane roads having homogeneous traffic by forming simple set of rules. In the present study, the arrival pattern, speed distribution, placement characteristics and acceleration characteristics of different types of vehicles are studied in field. A cellular automaton model is prepared based on NaSch model for a single lane road with one way traffic incorporating the observed conditions. The model considers two types of vehicles; cars and heavy vehicles. Three different cell sizes are used and results were compared to find out the optimum cell size, which represents realistic acceleration and deceleration rates. It was found that a cell size of 0.5m x 0.5m can best represent the field conditions. Further the model is extended for a two-lane one way road by adding overtaking maneuver. The simulation models are coded using VB 6.0 on a desktop computer. The performance of the model is validated by using field data and comparing the capacity value with that available in literature. Simulation runs are performed for different composition of traffic stream by varying the percentage of heavy vehicles and the results are presented in graphical and tabular form. Capacity of a single lane road is estimated 1100 veh/hr which reduces to 540 veh/hr in case of all HV situation. Similarly the capacity of a two-lane one-way street for all cars situation is estimated to be 1934 veh/hr and it reduces to 1336 veh/hr for all HV situation. The effect of HV on mean stream speed and PCU factor has also been evaluated.