ASSESSMENT OF ROADWAY CAPACITY FOR A FOUR- LANE DIVIDED ROAD UNDER HETEROGENEOUS TRAFFIC

Abstract

The economic growth of any country depends on transportation for its overall development. The highways in India follow heterogeneous traffic conditions in contrast to highways in other countries. Hence, the models developed for capacity estimation of highways by other countries cannot be adapted in India. In this paper, the assessment of roadway capacity for a 4-lane divided National highway-44 with two sections each of 60 meter stretch is identified and considered for the study. The sections were selected taking into account the effect of varying road geometry, pavement surface conditions and possible variations in traffic conditions only on normal weekday traffic. Traffic data consisting of classified traffic volumes, space mean speeds and free speeds of vehicles were obtained using videography technique in blocks of four hours each for 10 to 12 hours in a day to capture the effects of morning
and evening peak hours as well as the heavy traffic plying primarily in the night-time. The methodologies involved in this study are 1) free flow speed 2) Dynamic passenger car unit and 3) speed flow study. Speed-flow relationships on the study sections were then developed for the study sections and capacity flow was taken to be the traffic flow at half of the free flow speed at a section microscopic simulation of the traffic on the study sections was attempted using VISSIM 7.0. The simulation model was calibrated and validated using the observed volumes, space mean speeds. Subsequently the capacity was estimated using the speeds and flows obtained using the simulation model. The capacity with respect to four lane divided National highway is estimated to be around 4100 PCU/hr/lane/direction. Assessment of lane change behaviour for four-lane through field observations and model refinement can be done. Study can be extended to the estimation of Capacity for eight-lane and six-lane divided highways.