Integration of adaptive signal control and freeway off-ramp priority control for commuting corridors

Congestion at the downstream of an off-ramp often propagates the traffic queue to the freeway mainline, and thus reduces the freeway capacity at the interchange area. To prevent such potential queue spillover and improve traffic control efficiency over the entire corridor, this study develops an integrated control system which includes three primary functions: off-ramp queue estimation, arterial adaptive signal operations, and freeway off-ramp priority control. Using detected flow data, the system firstly estimates the queue length on the target off-ramp. If no potential queue spillover is predicted, the adaptive signal control function will then adjust the intersection signal timings and provide dynamic signal progression to critical path-flows. Otherwise, the off-ramp priority control function will be activated to clear the queuing vehicles at the off-ramp. To evaluate the effectiveness of the proposed system, this study has conducted numerical studies on a freeway interchange using a well-calibrated simulation platform. The experimental results reveal that the overall network performance can indeed be improved under the proposed control system, compared with other operational strategies. Further analyses of freeway time-dependent travel time distribution also evidence the effectiveness of the proposed system in preventing off-ramp queue spillover.