Influence of Carriageway Width and Horizontal Curve Radius on Passenger Car Unit Values of Two-lane Two-way Rural Roads

Capacity is a central concept in design and operation of roadways. Studying roadway capacity and factors affecting this capacity is an important issue when transportation facilities are designed or upgraded. One of the main components for the estimation of roadway capacity is the passenger car unit (PCU). The main objective of this paper is to study the influence of different geometric features of tangent and curved elements on PCU values on two-lane two-way rural roads. Geometry and traffic data were collected from six sites located on Benisuif-Assiut Agricultural Road, Egypt. Each site was composed of two elements; a straight element (tangent) and a succeeding horizontal curve. PCU values were estimated using the speed-area method. Using regression analysis, different models were developed to model the influences of different geometric features on PCU values. The results show that the PCU values for different vehicle categories increase linearly with increase of carriageway width and horizontal curve radius. This increase is clearly observed in case of heavy vehicles rather than light vehicles. The resulting models are useful in optimizing geometric design on two-lane two-way highways from the capacity point of view in the preliminary design stage