Effect of Road Roughness on Capacity of Two-Lane Roads

Abstract

The Highway Capacity Manual (2000) states that the capacity of a two-lane rural highway under ideal conditions is 3200 passenger car unit per hour for both directions combined. The ideal conditions as given in the manual do not include the riding quality of a road, which deteriorates with time. The present study has shown that the capacity of a two-lane rural road is also affected by the road roughness. Data collected on the roughness and free-flow speed of cars and heavy vehicles at a length of 55 km on three highways in India was used to establish the relationship between these two variables. Further, speed–volume data collected at eight different sections of two-lane roads were analyzed and the effect of road roughness on capacity was evaluated.