Evaluating the Speed-Flow Relationship of Urban Four-lane Roads under Heterogeneous Traffic Conditions

Sri Lanka has a rich road network of about 12,210km of A & B class roads, and over 31,000 km in the entire national road network. Of these, multi-lane roads cater to a major portion of the urban road network. Since they carry high traffic loads it is important to have a framework to evaluate the Capacity of these roads accurately. Since capacity values vary with the nature of the road and traffic stream developing indigenous capacity models is necessary. This research targets fill that gap by developing a speed-flow model for urban four-lane roads. In the process of developing this Passenger Car Unit(PCU) factors are developed for four-lane roads. The theoretical capacity for a four-lane road is found to be 2481 PCU/h/lane for 5-minute interval data. This is compared with the 15-minute interval capacity. Further the headway data of the survey sections were plotted and explored to have a better understanding of the nature of the traffic flow.