The dynamic control of automotive traffic at a freeway entrance ramp
✍ Scribed by H.N. Yagoda
- Publisher
- Elsevier Science
- Year
- 1970
- Tongue
- English
- Weight
- 735 KB
- Volume
- 6
- Category
- Article
- ISSN
- 0005-1098
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✦ Synopsis
Several "ramp metering" systems have been built to regulate the flow of automobiles onto freeways; a state model serves to exhibit the underlying control system dynamics and allows for system design and performance evaluation.
Summary--The work presented in this paper concerns the design and analysis of a dynamic control system for metering automotive vehicular traffic onto a high speed urban freeway. The problem treated involves the utilization of an automatic traffic controller that regulates the entrance flow of vehicles to a rate which minimizes the total expected delay experienced by vehicles entering the roadway, subject to the restriction that the entrance flow does not cause a breakdown of flow along the highway. The study is part of the Gulf Freeway Surveillance and Control Project conducted in Houston, Texas, for the United States Bureau of Public Roads, by Texas A and M University, and all experimental results were obtained from this project..~, Two criteria are considered in the mechanics of "ramp metering": One involves the insertion of entering vehicles into gaps, while the second involves metering vehicles into the stream at instants dictated by the margin between observed flow and highway capacity. In either case a stochastic state model is used to study the dynamic behavior of the control system. The state of the system is determined by the number of vehicles in the queue awaiting service in conjunction with the presence or absences of a trapped vehicle on the end of the merge area. Control is exercised by the release of vehicles, that are stopped and awaiting service, as is indicated by continuous monitoring of highway flow. The basic design parameter in the system is the threshold limit at which the next vehicle is released, provided that the previously released vehicle has completed its merge. In all, several designs were investigated including: a fixed control system, with a predetermined threshold; a programmed control system, in which the threshold is varied as a function of time; and a feedback control system, in which the threshold is varied as a function of the average stream volume. The resultant control systems were or are being implemented and tested on the Gulf Freeway.