Merging Lane Length for Expressway Improvement Plan in Japan

Expressway networks in large urban areas are often tied up with increasing traffic demands from many large commercial vehicles. These traffic conditions are preventing the expressway networks from their original function of rapid and steady transport. Bottleneck sections on expressways are now being investigated to improve the situation. This report describes a traffic survey and an analytical method to determine the necessary merging length for an improvement project for the Meishin Expressway near the Tennozan and Kajiwara Tunnel. A probabilistic theory for calculating the merging lane length was developed, and the theory was applied to the expected traffic and geometric conditions of the improvement plan. A series of traffic surveys were conducted to estimate the traffic flow characteristics of the merging lane and the drivers' behavior when they are merging with traffic at high speeds. The merging lane length was determined based on the results of the traffic survey.