Evaluation of planning options to alleviate traffic congestion and resulting air pollution in Dhaka city

Abstract

Traffic congestion has now become a very serious problem particularly in metropolitan Dhaka, the capital of Bangladesh. Because of the rapid socio-economic changes and increase in population, the city expanded dynamically without any planning and control. Such rapid and uncontrolled developments have created an unacceptable level of disparity in the transportation demand and supply scenario, which resulted in traffic congestion and environmental degradation through air pollution. To reach at an equilibrium level between the demand and the supply, it is required to implement traffic engineering and transport planning measures on the basis of scientific studies. Considering the grievousness of the situation, concerned authorities like Bangladesh Road Transport Authority (BRTA), Dhaka Metropolitan Police (DMP), Dhaka Transport Coordination Board (DTCB) and Bangladesh Road Transport Corporation (BRTC) have taken several measures for its improvements. But these were implemented in ad-hoc and disintegrated way thereby failing to achieve the desired result. In fact to tackle the problems of increasing traffic congestion and resulting air pollution, quantitative analyses of the situations are deemed necessary and the plans should be designed on the basis of the results of analyses. This study is devoted to analyze present and future traffic congestion and resulting air pollution in Dhaka city. In the study, a few immediately feasible alternative planning options are considered for evaluation which include elimination of rickshaw and autorickshaw, improvement of road network, improvement of bus transit and introduction of rail transit system in Dhaka city. In this regard a transportation model, named as 'Dhaka Urban Transportation Model' (DUTM) has been developed and calibrated for the study area. The area included in this study comprises 154 km1 of central urban portion of Dhaka city, which is the area under jurisdiction of Dhaka City Corporation. This area includes 90 wards of Dhaka city Corporation with population of around six million and 350 kilometer roadway of the city. DUTM is used to simulate the peak period hourly traffic volume on roadway links within the study area. In this study, traffic congestion is evaluated by using four types of congestion indices and air pollution is evaluated by emission rates of SO" NOx and CO in ton per hour. The congestion indices used in this study are Roadway Congestion Index (RCI), Volume Capacity Index (VCI), Travel Rate Index (TRI) and Congestion Severity Index (CSI). For the present year of 2002, it is found that peak period total travel demand is 1.3 million vehicle-km and 59.5 thousand vehicle-hours. These demands increase exponentially with the increase in city population. At present 24% of total roadway length of the network carries peak period traffic with average speed less than 5 kilometer per hour, 62% of total roadway length carries peak period traffic with volume-capacity ratio greater than 1.25, the total travel demand exceed the total network capacity by 250 percent and 227 hours delay occurs per 1000 kilometer travel. The emissions of SOx, NOx and CO are 0.3 ton per hour, 0.8 ton per hour and 13.5 ton per hour respectively. The analyses have been extended up to the planning period of 2020 for business as usual case, called the baseline analysis, as well as for the alternative options. In the baseline analysis, it is found that the percentage of roadway length with peak period traffic having average speed less than 5 kilometer per hour will increase to 42.5% in 2010 and to 58% in 2020. The total travel demand will exceed the total network capacity by 343 percent in 2010 and by 460 percent in 2020. The delay per 1000 kilometer travel will increase to 937 and 3575 hours in 2010 and 2020 respectively. The emission of SOx, NOx and CO will increase to 1.3,4.1 and 62 ton per hour in 2020 respectively. The evaluations of planning options imply that elimination of rickshaw reduces traffic congestion by more than 50 percent and reduces delay by more than 90 percent. It also reduces emission of SOx, NOx and CO by more than 50 percent in the long run. The effect of the elimination of auto-rickshaw on traffic congestion is not significant, but it reduces emission of SOx and CO by more than 20 percent. Although the elimination of rickshaw and auto-rickshaw will result in considerable reduction in both traffic congestion and air pollution, in order to sustain the level of mobility, it is required to increase the number and quality of buses substantially. In connection with the improvement of the bus service, the study suggests that the improvement of the speed will be the most beneficial. In the study, it is observed that the significant increase in network traffic flow can be achieved through minor improvements at a few bottleneck points in the road network of the city. The feasibility of introducing rail transit using the existing surface rail lines of the Dhaka city is also examined in this study. The result implies that a system of rail network will be required in order to make it a feasible alternative. The results also suggest that the rail transit system will require suitable access modes to extract the optimum benefit.