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

Mehdi Fallah Tafti

doi:10.2174/1874447801812010230

Abstract

Aim: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.Methods: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.Results: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.Conclusion: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.

Highlights

Freeways and expressways around the world are commonly suffering from general problems of congestion, poor safety and high environmental impacts
An example of speed limits set by the coordinated Variable Speed Limit (VSL) and Ramp Metering (RM) system in relation to the actual traffic speeds measured at the detector position is shown in Fig. (5)
A general overview of the results presented in Table 2 indicates that whilst the mainline average travel time has been increased under the RM only control scenario, it has been reduced under the combined RM+VSL control scenario

Summary

Introduction

Freeways and expressways around the world are commonly suffering from general problems of congestion, poor safety and high environmental impacts. Various traffic management and control systems such as Ramp Metering (RM) and Variable Speed Limit (VSL) control systems have been proposed and implemented to address these issues Each one of these systems intend to achieve specific objectives which may or may not be consistent with the objectives set for other control measures deployed in the same freeway or expressway area. IN VISSIM, ramp metering can be modelled either using the built-in fixed-time control or an optional external signal state generator. VAP (Vehicle Actuated Programming) is an optional add-on module of VISSIM for the simulation of programmable, phase or stage based, traffic actuated signal controls [35]. This module is programmable with a simple descriptive language. Interprets control logics, and creates signal commands on a discrete time step basis

Objectives

Methods

Results

Discussion

Conclusion