Merging Lane Length for Expressway Improvement Plan in Japan

The investigation is reported of the merging lane length needed for an improvement section between Kyoto South and Suita on the Meishin Expressway, Japan. 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. It was concluded that the merging lane length for the transition section between the same directionally divided 4-lane section and the normal 3-lane section should be 700 m. However, in order to make the merging length calculation more generally applicable, the following need to be investigated: percentage of drivers who change lanes to allow vehicle to merge in different traffic and regional conditions; the possibility of including other important variables such as acceleration and deceleration rate, etc.; gap acceptance for the median side merging vehicle.