Traffic assignment model for simulation and optimization of road network

Abstract

Optimization of traffic and accurate assessment of traffic volume on different roads are very important in transportation planning. Optimization of traffic provides the advantage of best utilization of an existing facility. A balanced transport system, which ensures minimum user cost on every route, also depends on traffic optimizatio~. The design of road layouts and pavements and analysis of alternative highway projects are based on an assessment of traffic volumes in a balanced condition. This study attempts to make an independent approach in the field of traffic assignment. It computerizes a traffic assignment model and tends to combine mathematical analysis with subjective judgement in order to develop a method that is reliable and easy to use in road transport planning. The term 'subjective judgement' implies a choice in flow - travel time relationship and modelling of delays at road intersection. A procedure has also been developed to assess the impact of any new road link on traffic flow over an existing road network. Major features of the model include a computerized procedure for finding quickest route between any trip origin and trip destination in a road network, implementing an iterative procedure for the assignment of traffic and developing a method for the assessment of impact. The model was developed by remodelling Ford-Fulkerson' s analytical algorithm of quickest route finding for computerization and capacity restraint traffic assignment algorithm. The impact was measured in terms of travel impedance viz. travel time and passenger car unit- minute . The model is based on data of network structure and origin- destination (00) matrix. It can be used to estimate the traffic volume on any road link should a change occur in the network structure or in the origin- destination (00) matrix. Statistical analyses showed that the result obtained from the model developed in this study agree very well with the practical situations. The model was applied for traffic analysis of the road network in metropolitan .Dhaka. In particular, the effect of 'Pantha-path' extension, a new road under construction connecting Green road with Mirpur road, was studied. It was found that this new road will provide nearly nineteen percent reduction in overall travel time required by all the vehicles to travel within the study area at peak hour. Individually, the link travel-time reductions varied between 15 and 196 percent. A step wise procedure to obtain the future traffic volumes on different road links by using this model is presented to assist the user in the model's application.