Estimation of Capacity for Two-Lane Inter-Urban Roads in India using Free Speed Data

Estimation of capacity is one of the fundamental requirements for designing, operation and layout planning of a road network system. One of the fundamental concepts of traffic flowtheory and estimation of road capacity is the free-flow speed. It is referred to a condition where vehicle movement is not influenced by presence of other vehicles in the stream. Under such condition, the free speed of a vehicle represents the overall roadway condition. From HCM (2010) it is indicated that the capacity is influenced by free flow speed. However, such influence is not quantified for two-lane inter-urban roads. Most of thecapacity estimation methods require extensive data collection and high man-hour budget allocation. Traffic on Indian highways is heterogeneous and lane discipline is very poor, making simulation techniques very difficult to apply. On the other hand, other capacityestimation methods generally consider homogeneous traffic stream. Under such circumstances, PCU values are used to convert a heterogeneous traffic to a homogeneoustraffic. Since PCU values are dynamic and single sets of such values are not applicable to varying traffic conditions, such procedure requires extensive data collection handling of which is complicated, expensive and time consuming. The objective of this study is to propose a model which provides a quick estimation of capacity by removing the complexities, while accuracy is maintained.

Keywords:

Capacity , two-lane roads , operating speed , heterogeneous traffic , passenger car unit