Optimum Capacity of Freeways: A Stochastic Approach

This study explores a practical value for highway capacity that is able to represent stochastic capacity and optimize the performance of designed facilities. Optimal performance of roadways could be defined in terms of cost, safety, reliability, and vehicle throughput. We optimize the performance of freeway facilities using the traffic efficiency concept and maximizing vehicle throughput. Traffic efficiency, which is a combination of flow rate breakdown probability and capacity drop, is determined for one of the major freeways in Tehran, Iran. We depict flow-efficiency diagrams for freeway sections to extract the optimum capacity. Comparing the proposed optimum capacity and conventional capacity, we suggest the design value of capacity as 90% of conventional capacity values. The proposed optimum capacity in this study insures the maximum vehicle throughput in designed facilities. (C) 2018 American Society of Civil Engineers.