EFFECT OF LANE WIDTH AND SURFACE CONDITION ON CAPACITY OF TWO LANE ROADS

Abstract

Prediction and knowledge of capacity is fundamental in design, planning and layout of highways. Among other things, it provides the basis for determining lane width and number of lanes to be provided at any point in a road network with respect to volume and composition of traffic. It is a valuable tool for evaluation of the investments needed for future road construction and improvements. The factors affecting the capacity of road are physical roadway conditions, traffic conditions, control conditions and weather conditions. In present analysis, an attempt has been made to determine the effect of lane width on PCU of different type of vehicles and thereby capacity of two-lane roads. The variation in speed with surface conditions (thy, wet and rainy) is also analysed. Data collected at seven• sections of two lane highway with varying carriageway width (5.5 to 9.0 m) has been analysed to capacity of two-lane roads. It is found that PCU of vehicles increases with increasing lane width. Capacity also increases parabolically with lane width. It increases by 450-550 pcu/hr for every one meter increase in total width of carriageway. Further data collected at three road sections to estimate the effect of surface conditions (dry, wet and rainy) on speed indicated that the speed of a vehicle generally decreases by 10-18 percent in wet conditions and 20-30 percent in rainy conditions. Effect was more pronounced on speed of 3-Wheelers less pronounced on 2-Wheeler as compared to other vehicles.