NEW METHODS OF CAPACITY DETERMINATION FOR RURAL ROADS IN MOUNTAINOUS TERRAIN

A highway need study was conducted in west virginia by reviewing speed studies on highways throughout the state. The operating speed on an existing highway is affected by design speed, traffic volume, and number of lanes. Also, for 2-lane roads, it is affected by the availability of sections on which the sight distance is of sufficient length to perform passing maneuvers safely. In the design of a new highway, it is the one factor which together with the traffic volume and assumed design speed determines the needed geometric features of a highway. An engineering analysis of the highway capacity requires the following information: (1) type of terrain through which the highway is located, (2) average highway speed and frequency of occurrence of sharp curves that cause abnormally low speeds, (3) percentage of the highway on which the passing sight distance exceeds 1500 feet, (4) the average truck factor and the truck factor on all long or steep grades, and (5) cross-section items such as shoulder and surface type, width, and condition. These items were determined for all highways in west virginia expected to carry annual volumes in excess of 1800 vehicles per day within the next 20 years.