The prevailing roadway and traffic conditions on Expressways, in India are vastly different as compared to the other roads in India and additionally, there is no perfect, strict lane discipline. Nevertheless, there is not much research literature available specific to these categories of roads in India. The knowledge of roadway capacity is an important basic input required for planning, design, analysis and operation of roadway systems. Hence, this work aims to model traffic flow on Indian urban expressways with specific reference to Delhi- Gurgaon Expressway and estimate its capacity using the micro-simulation model using VISSIM 5.40. For this purpose, the field data collected on traffic flow characteristics on expressways was used in calibration and validation of the simulation model. The validated simulation model was then used to develop fundamental traffic flow relationships, namely, speed-flow, speed-area occupancy, and flow-area occupancy for the traffic flow levels, starting from near-zero until capacity of the facility. The capacity of an eight-lane divided urban expressway in level terrain with 14.0 m wide road space (one direction of traffic flow) was found to be in the range of 9700 to 10000 vehicles/hour. In this study, through sensitivity analysis using simulation model, the following relationships: (ⅰ) percentage trucks in the traffic stream and capacity-level flow, and (ⅱ) percentage of trucks in the traffic stream and capacity level traffic-stream speed, were also developed. The outcome of the study also ensures the fact that the area-occupancy is an appropriate measure of traffic concentration for prevalent roadway and traffic conditions in developing countries like,-India. The results and the overall methodology followed in this study for modeling traffic flow on Expressways in India to determine the capacity estimates, under varying traffic compositions may be very useful for the practitioners and also for the ongoing efforts to prepare an Indian Highway Capacity Manual.
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