Freeway congestion management using ramp metering with consideration of diversion

The objective of this research is to develop a congestion management system for freeway corridors. The freeway traffic flow management system consists of three major components: a macroscopic traffic flow simulation model which realistically describes the traffic flow behavior on freeway corridors; an optimization algorithm which determines optimal ramp metering rates at on-ramps according to the traffic conditions obtained from the simulation model; and a traffic diversion scheme which takes into account diverted traffic and its impacts on adjacent arterials. A section of the I-64-40 corridor in the St. Louis metropolitan area was selected as the study site. A traffic flow simulation model was developed by utilizing finite differences techniques. A nonlinear speed-density model was constructed as a major component of the simulation model. The simulation model takes into account the impact of weaving movements, resulting in great accuracy in describing the traffic dynamics. The ramp metering optimization algorithm was formulated as a nonlinear programming problem. The optimization algorithm is capable of determining the optimal ramp metering rate with respect to the real-time traffic condition. The results indicate that the implementation of ramp metering control can effectively alleviate freeway congestion. A traffic diversion scheme was developed in conjunction with the ramp metering control strategies. The optimization of the traffic operation on the surface street network was achieved through a traffic assignment and signal timing optimization. It was found that current traffic conditions on the surface street network could be significantly improved through signal timing optimization. The resulting new signal timing plans not only are adequate to accommodate the additional traffic due to ramp metering control, but are also effective in improving overall traffic operation. The freeway congestion management system shows that the congestion on a freeway corridor and surface street network can be alleviated simultaneously by the implementation of appropriate ramp metering, traffic diversion, and arterial signal timing strategies.