A Study on the Merits for Coordinated Use of Ramp Metering and Variable Speed Limit Traffic Control Systems

Mehdi Fallah Tafti*
Department of Civil Engineering, Faculty of Engineering, Yazd University, Yazd, Iran

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Creative Commons License
© 2018 Mehdi Fallah Tafti.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address Correspondence to this author at the Department of Civil Engineering, Faculty of Engineering, Yazd University, Yazd, Iran; Tel: +98-3531232469; E-mail:



The aim of this research was to investigate the merits for further improvements of traffic operation on freeways and expressways through coordinated use of Ramp Metering and Variable Speed limit (VSL) control systems.


In this research, the widely used ALINEA Ramp Metering strategy was coordinated with a rule-based VSL strategy so that the total flow entered from the upstream freeway and entry ramp is maintained below the merge downstream capacity. The developed algorithm was then examined on a freeway network comprising two merge and one diverge sections, using VISSIM microscopic simulation model. The performance of the simulated network was examined under three scenarios namely, No-control, Ramp Metering only and Ramp Metering plus VSL controls. The network performance under each scenario was then assessed and compared using three measures of performance namely, average travel time, overall delay and freeway throughput. The ANOVA test was used to analyze and compare the impacts of specified scenarios.


The results indicated that the best performance is achieved under coordinated Ramp Metering plus VSL scenario as it produced a significantly better performance in comparison with the other two scenarios.


The results can be attributed to the synergistic effects of coordinated and integrated use of these control systems on the freeway network and therefore, coordination of such systems is recommended.

Keywords: Freeway Traffic Management Systems, Coordinated Traffic Control Systems, Integrated Traffic Control Systems, Ramp Metering, Variable Speed Limit Control, Controlled Motorways.