A dynamic system-optimum control model for commuting traffic corridors

The need to implement effective traffic control in commuting corridors has long been recognized by transportation professionals. However, most existing studies focused either on optimizing freeway ramp metering rates or providing coordinated surface street signals, without taking account of the vital interaction between these two subsystems. As a result, it is not unusual that an effective control strategy for freeway operation may cause significant detrimental effects to the adjacent surface streets. On the other hand, the access to freeway ramps is often impeded by the formation of congestion or bottlenecks on surface streets due to the increasing peak-period traffic demand and ineffective signal operation. This paper presents a dynamic system-optimal control model (DSOCM) for commuting corridors which consist of both freeway and surface street segments. The proposed DSOCM considers the complex interactions among the freeway, surface street and diversion flows, and allows the system operators to compute the optimal time-dependent ramp metering rate and signal setting over the selected time horizon. Depending on the input reliability, DSOCM need not be executed at every control interval as long as the differences between the projected and actual traffic conditions are within the acceptable range. An effective and coordinated control operation for integrated traffic systems can then be achieved.