AN INTEGRATED REAL-TIME INTERCHANGE CONTROL SYSTEM

Abstract

Contending with various recurrent congestion patterns on major freeway corridors has long been the priority task of the transportation community. Most of such patterns take place on a freeway interchange’s on-ramp and off-ramp segments where both exiting and merging flows often trigger series of lane changes and resulting in significant freeway speed reduction, and propagation of traffic queues to neighboring surface streets. To address such critical issues, this study has developed an integrated real-time interchange control (IRIC) system, which includes an integrated off-ramp signal control (IOSC) module, an off-ramp queue impact (OQI) model, a lane-group-based (LGB) traffic model, and a ramp metering as well as arterial signal optimization modules to concurrently mitigate freeway traffic congestion and minimize any negative impacts on the nearby local arterials.The primary objective of the IOSC module is to account for the impacts of off-ramp queues on the freeway’s traffic conditions in design of the off-ramp signals. Its embedded OQI model functions to provide the impact information of the off-ramp queues on the freeway for signal optimization, and its LGB model aims to project the freeway’s lane-by-lane speed variation due to the on-ramp merging traffic. The developed IOSC is further integrated with innovative on-ramp metering and arterial multi-path progression models to constitute an integrated real-time interchange control system that can produce the optimal time-varying ramp metering rate and signal plan for both the off-ramp intersection and the arterials within the impact boundaries of a freeway interchange. The evaluation results from extensive experiments, conducted with a customized interchange simulator, have confirmed the effectiveness of the developed real-time interchange control system, especially with respect to its capability of preventing ramp queue overflows to the neighboring arterials and minimizing the off-ramp spillback onto the freeway mainline.