Localized Switching Ramp-Metering Control with Queue Length Estimation and Regulation and Microscopic Simulation Results

In this paper, we first review a localized ramp-metering strategy for freeways that achieves the goal of reducing the spatial and temporal span of traffic congestion, using locally available information. The control scheme is composed of a switching mainline-traffic responsive ramp-metering controller that adapts to the different traffic dynamics under different congestion conditions---free-flow or congested---and a queue length regulator that yields improved performance over the currently used ad hoc ``queue-override'' scheme and prevents the queue from exceeding the ramp storage capacity. Subsequently, a queue length estimator is designed to provide feedback to the queue length regulator, using the queue-detector speed data that are available in the field. Test results on a calibrated microscopic traffic simulator demonstrate the performance and effectiveness of the switching ramp-metering controller, the queue length estimator and regulator, and the overall control strategy. The Total Vehicle and Passenger Delays are both reduced by 16%, while the Total Vehicle Time and the Total Average Vehicle Speed are improved by 5.6% and 5.8%, respectively. As a comparison, simulation results of ALINEA are also presented.