Integrating Roadside Speed Control with Ramp Metering

Traffic congestion on freeways is a serious problem in most countries, with manifold adverse effects − from lost vehicle hours, fuel overuse to emissions. Empirical researches have attributed higher traffic demand, bottlenecks and disturbances from individual driver behaviour as the key interplaying causes for a breakdown in traffic. As adding extra infrastructure on one hand is often dismissed as a financially or spatially unviable alternative, and on the other has been scientifically known to induce more demand, traffic management and control have assumed great importance today.

Dynamic control using variable speed limits (VSL) has been a promising approach for mainstream control of traffic to prevent and resolve traffic jams. VSLs have been shown to be effective in theory, simulation and field experiments. However, deployment of these systems in full-scale and in an integrated way still faces practical issues. One of these is the integration of VSLs with ramp-metering control. On-ramps are intermediate road infrastructures that offer access to the freeway at different locations along its length. The merging of the two streams of traffic at such locations can, however, triggers local instabilities. In cases when the freeway speed control system is ordered in the spatial reach of an on-ramp, additional flows and merging inefficiencies can hamper the efficacy of the system and in worse cases, stall its activation. 

COSCAL (Cooperative Speed Control Algorithm) is a feedback control approach with an analytical framework based in shockwave theory. The control system aims at resolving wide moving jams by earliest detection of jam, and uses speed limitation to resolve congestion and stabilize traffic. This research first looks at the implementation of a macroscopic version of this algorithm, with roadside deployment. Following which,a ramp metering strategy with queue management will be integrated with this speed control algorithm. Finally, the functional effectiveness of the controller, with the designed adaptations, will be tested in VISSIM micro-simulation package.

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