SPACING OF INTERSECTIONS IN HIERARCHICAL ROAD NETWORKS

This paper presents an analytical model for examining the spacing of intersections that connect different levels of roads in a hierarchical network. An analytical expression for the average travel time is obtained for a grid road network with two road types: minor and major roads. The travel time is defined as the sum of the free travel time and the delay at intersections. The analytical expression gives basic properties of the tradeoff between the travel time on minor and major roads. The optimal pattern of intersections that minimizes the average travel time is then obtained. The result demonstrates how the road length, the intersection delay, the travel speed, and the size of the city affect the optimal pattern. The model is also applied to the road network of Tokyo. The proposed model explicitly considers the tradeoff between the accessibility to higher level roads and the delay at intersections, and is useful for hierarchical road network design.