Effects of the Number of Lanes on Freeway Traffic Characteristics in Empirical Observations and Microscopic Simulation

Methodological gaps exist in the literature on analyzing the relationship between freeway traffic characteristics and the number of lanes. This paper focuses on the effects of the number of lanes on traffic characteristics. This is done by empirical observations and microscopic simulation. The empirical research is validated upon the extensive field survey of traffic flow in Beijing and Shanghai. The findings show that, under free-flow conditions, vehicle velocity increases slightly with increasing number of lanes on uninterrupted freeway segments; whereas under congested conditions, both flow rate per lane and vehicle velocity decrease marginally as the number of lanes increases. Based on the difference among the speed-density relationships, two different arguments on whether building a wide road or a number of narrow roads are interpreted. In microscopic simulation, an improved lane-changing model is proposed. Both the lane-changing implement process and the impact of the lane-changing vehicle on the adjacent vehicles are incorporated into the proposed model. The simulation model is used to validate the difference in traffic characteristics on freeways with different number of lanes. In addition, the simulation results that maximum reserved capacity per lane decreases with the increasing number of lanes on freeways, and that the change of lane-changing activity and its associated disturbance to traffic stream causes significant differences in traffic operational characteristics on freeways with different number of lanes. The exposition of essential difference will convincingly implicate that the manuals of traffic engineering should be revised for the better plan, design, and control of road network.