Development of a GIS-based model for optimum traffic flow distribution a case study on selected major routes of Dhaka City

Abstract

Traffic congestion is a part of daily life routine envisaged in mega city Dhaka. The urban transport system is confronted with a big challenge to cope up with excessive population growth resulting outstripped its capacity. Transport situation in Dhaka is characterized by traffic congestion and delays, poor traffic management and fast growing air pollution problems. Besides, faulty traffic signalling systems, inadequate manpower, narrow road spaces and overtaking tendency of drivers create pro-longed traffic congestions. Due to traffic congestion a substantial portion of working hours have to be left on streets. With rapid urbanization, congestion will only worsen the prevailing situation in the absence of effective planning. Traffic congestion has increased significantly in urban areas of Dhaka city where the growth in volume of motorists has risen faster than the growth in roadway capacity. To develop an optimal transportation system an estimation of optimum traffic flow is necessary. Optimum traffic flow distribution is defined as traffic rate allocation based on network utility maximization. In this context scenario is somewhat different in Bangladesh, here in Dhaka city vehicular emission and roadway capacity issues are more important than least travel cost and travel time as there are not so many alternative options (both road and vehicle mode) to the road users. Reducing congestion will reduce automobile emissions, and thus urban air pollution, which is currently posing a major health threat in most megacities like Dhaka. However, no study has been conducted yet to develop a traffic flow distribution model considering travel demand. In this context, firstly an attempt has been made to study the existing travel demand along some major routes of Dhaka city. The GIS-based model would be developed to optimize traffic flow in some selected major roads of Dhaka city by keeping pollution level within an acceptable limit (according to ECR, 1997) and not exceeding road type capacity (according to DITS,1994) and also to occupy additional traffic flow along existing alternative route in order to reach the same destination. To examine the travel demand of vehicle users along the study routes, cordon survey (O-D survey) through direct interview method has been conducted under field work. For the detail analysis the selected major roads have been divided into four major routes viz. 1) Mirpur Road, 2) Pallabi to Gulistan, 3) Kuril to Bijoyshoroni and 4) Kuril to Shegunbagicha. Detail analysis has been conducted and photographs have been provided to portray the scenario. For convenience of analysis total study area has been divided into some Traffic Analysis Zones (TAZs). After thorough analysis of the primary and secondary data some findings have been summarized. Land use demand estimation has been conducted along the major routes of Dhaka city. Through this, existing travel demand has been explored. Roads with excessive vehicular pressure have been identified. A reason behind this excessive congestion has shown to be due to some specific land uses which play predominant role and located along and nearby these routes. From travel demand estimation, dominance of specific TAZ as origin and destination of most of the trips made has been identified. Vehicle mode wise dominance of TAZ has also been identified. Calculation of land use demand for different TAZ has also been performed. From O-D survey findings output matrix has been developed consisting percentage of vehicles starting from an origin and going into particular destination to serve specific purpose along each of the thirty five study links. Besides this, route identification for each category vehicle (% of vehicle classes going into which destination along specific route) has also been done. Also travel behaviour analysis has been conducted under the study. After that, optimum traffic volume has been computed for each route using GIS based Geo processing option (python coding) to depict the ideal number of traffic suitable for each route through satisfying two important criteria: vehicular emission and roadway capacity which are very significant variables in the context of Dhaka city. Finally, as travel demand cannot be neglected and must be satisfied, for this reason alternative route are being used to accommodate additional vehicles to reach their original destination. On the basis of these findings some specific recommendations have been made to reduce traffic congestion and to improve public health through ensuring a smooth travel to the vehicle (both motorized and non-motorized) and road users of Dhaka city.