EFFECT OF GRADIENT ON CAPACITY OF TWO LANE ROADS

Abstract

Capacity analysis is fundamental to planning, design and operation of roads. Among other things, it provides the basis for determining the number of traffic lanes to be provided for different road sections having regard to volume, composition and other parameters of traffic. The factors affecting the capacity of road are physical roadway conditions, traffic conditions, environmental conditions and control conditions. The traffic stream in India and many other developing countries consists of two distinct categories of vehicles namely, fast moving vehicles and slow moving vehicles. The static and dynamic characteristics of these two type of vehicles vary widely. Invariably the same right of way is used for the movement of both types of vehicles. Because of large size of commercial vehicle, heavy load they can-y, poor operational performance and wide speed differential, they cause delay to the following vehicles. As a result the capacity of highway is adversely affected. In this thesis, an attempt has been made to determine the effect of gradient on speed of different type of vehicles on two-lane roads. The effect of gradient on PCU of different categories of vehicles and thus capacity of two-lane roads is analysed. Data collected at different sections of highway with varying gradient conditions have been analysed to determine the effect of gradient on capacity of road, PCU and free speed of different type of vehicles. The speed-volume relationship for all the roads (having different gradient) has*en established. The capacity of two-lane two-way road on level is estimated as 2620 PCU/hr. It is observed that every one percent of upgrade decreases the capacity by 2.61% and every one percent of downgrade increases the capacity value by 3.09%.