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

Aim:The aim of this research was to investigate the merits for further improvements of traffic operation on freeways and expresswaysthrough coordinated use of Ramp Metering and Variable Speed limit (VSL) control systems. Methods:In this research, the widely used ALINEA Ramp Metering strategy was coordinated with a rule-based VSL strategy so that the totalflow entered from the upstream freeway and entry ramp is maintained below the merge downstream capacity. The developedalgorithm was then examined on a freeway network comprising two merge and one diverge sections, using VISSIM microscopicsimulation model. The performance of the simulated network was examined under three scenarios namely, No-control, RampMetering only and Ramp Metering plus VSL controls. The network performance under each scenario was then assessed andcompared using three measures of performance namely, average travel time, overall delay and freeway throughput. The ANOVA testwas used to analyze and compare the impacts of specified scenarios. Results:The results indicated that the best performance is achieved under coordinated Ramp Metering plus VSL scenario as it produced asignificantly better performance in comparison with the other two scenarios. Conclusion:The results can be attributed to the synergistic effects of coordinated and integrated use of these control systems on the freewaynetwork and therefore, coordination of such systems is recommended.