City-wide traffic control: Modeling impacts of cordon queues

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City-wide traffic control: Modeling impacts of cordon queues

Ni, Wei / Cassidy, Michael

Highlights • Neighborhood MFDs are re-scaled to account for effects of cordon queues. • Simulation experiments reveal that re-scaled MFDs better predict traffic performance. • Cordon-metering plans are found to be more effective as well.

Abstract Optimal cordon-metering rates are obtained using Macroscopic Fundamental Diagrams in combination with flow conservation laws. A model-predictive control algorithm is also used so that time-varying metering rates are generated based on their forecasted impacts. Our scalable algorithm can do this for an arbitrary number of cordoned neighborhoods within a city. Unlike its predecessors, the proposed model accounts for the time-varying constraining effects that cordon queues impose on a neighborhood’s circulating traffic, as those queues expand and recede over time. The model does so at every time step by approximating a neighborhood’s street space occupied by cordon queues, and re-scaling the MFD to describe the state of circulating traffic that results. The model also differentiates between saturated and under-saturated cordon-metering operations. Computer simulations of an idealized network show that these enhancements can substantially improve the predictions of both, the trip completion rates in a neighborhood and the rates that vehicles cross metered cordons. Optimal metering policies generated as a result are similarly shown to do a better job in reducing the Vehicle Hours Traveled on the network. The VHT reductions stemming from the proposed model and from its predecessors differed by as much as 14%.