Assessment of Capacity and Flow Improvements of Combined Dynamic Signal Control and Dynamic Speed Limits in Signalized Networks

Capacity and traffic flow advantages of combined dynamic signal control and dynamic speed limits for signalized networks are assessed. First, a new traffic signal and speed limit control and queue management algorithm is formulated. The algorithm combines dynamic signal control with dynamic speed limit selection to obtain near-optimal traffic control and management schemes. Speed limits and signal timing parameters (cycles, green splits, and offsets) are all time-dependent decision variables. The control capabilities of the new algorithm are explored and their impacts on the quality of traffic flow and capacity utilization are quantified through different measures of effectiveness. Genetic algorithms are used to obtain near-optimal control solutions for a hypothetical grid network. Numerical evaluations of control under different settings showed that: 1) selected speeds resulted in more efficient offsets, especially for dependent links, 2) queues are managed appropriately throughout the network such that spillbacks are prevented, and 3) improvements over fixed speed limit control were more pronounced for larger networks. The new control algorithm can be employed in advanced traffic management systems. Its implementation in real world networks requires closed-loop control setup with reliable traffic information.