Mathematical analysis of effects of lanes' number on expressway capacity

Methodological gaps exist in the literature on analyzing the relationship between expressway capacity and the number of lanes. Based on extensive field survey of traffic flow in Beijing, the findings show average capacity per lane decreases with increasing number of lanes on uninterrupted expressway segments. An explanation and trend of the decrease are analyzed upon the mathematical analysis. The rationality of the explanation is validated by the surveyed data. It reveals that the increase of lane-changing activity and its associated disturbance to traffic stream causes significant reduction in average capacity per lane on freeways. The results of the researches are the background support that tends to revise the highway capacity manuals, optimize planning and design of road network, and improve supervision and control of traffic network.