A Freeway Heuristic Control Method Based On Ramp Queue Length Constraints

With the stable growth of freeway traffic volume, traffic congestion occurs continuously. In order to solve the problem of main line congestion and on-ramp queue overspill, a new method is put forward for modern freeway control that an improved heuristic control method based on ramp queue length constraints is proposed which can determine the real-time number of the coordinated ramp and predict the dynamic critical occupancy accurately.Rules of determining the coordinated ramp are designed according to the traffic operational condition of main line and ramp queue length. The real-time number of the coordinated ramp group can be determined which can expand the storage space of the coordinated ramp group and release the pressure from main line congestion.The prediction algorithm of critical occupancy can be designed using the real-time detection data of traffic volume and occupancy in the downstream of the on-ramp. The dynamic critical occupancy will be part of the heuristic control strategy which can adapt to the change of the critical occupancy with respect to changing environment conditions maximizing main line traffic throughput.Microscopic simulation software named VISSIM is used in this paper to build a virtual road segment along the Yangtze River. The evaluation is conducted by network performance, traffic operational condition of downstream merge areas and equity of the ramp. Improved heuristic control strategy can improve the total network 3.4% compared with the control method based on ramp queue length constraints. Occupancy in the merge area is maintained around the dynamic critical occupancy and traffic volume in the merge area increase 1680veh/h under the changing environment conditions. It can maintain the average delay time and the relative queues at coordinated ramps close to each other which ensures the equity of the ramp.The improved heuristic control method proposed in this paper is fit for coordinated ramp metering under traffic congestion which can not only maximize main line traffic throughput but also prevent on-ramp queue overspill.