Integrated variable speed limit and ramp metering control study on flow interaction between mainline and ramps

Xu Wang,Lei Niu

doi:10.1177/1687814019831913

Abstract

During peak periods, bottlenecks are often triggered by excessive demand from both on-ramp and mainline input flows. To relieve bottleneck severity and improve traffic safety, ramp metering and variable speed limit are implemented to control the on-ramp and mainline input flows, and sometimes they are integrated. This article presents a proactive integrated control, with goals to save network-wide travel time and increase traffic flow. A METANET-based macroscopic traffic model was adopted as a prediction model. Micro-simulation tests were performed to evaluate and compare the control approaches among integrated and isolated control scenarios. By decoupling the traffic prediction and simulation models, the control error sources were analyzed. The evaluation revealed that both isolated and integrated controls benefit the traffic network to different extents under varying demand scenarios. Under proactive integrated control, ramp metering is activated solely during slight congestion; or it is activated during high-congestion periods to assist variable speed limit and thus integration maximizes the infrastructure utility.

Highlights

Active traffic and demand management (ATDM) methods, including ramp metering (RM),[1,2] variable speed limit (VSL),[3,4] and route guidance (RG)[5] effectively and efficiently alleviate freeway congestion and improve traffic safety
The applied integrated control of RM and VSL aims to achieve optimal network performance according to traffic states predicted in real time
The overall mobility performance is improved by VSL at bottlenecks but lowered at upstream segments; (b) RM limits flow by stopping on-ramp vehicles at entrances to the freeway mainline

Summary

Introduction

Active traffic and demand management (ATDM) methods, including ramp metering (RM),[1,2] variable speed limit (VSL),[3,4] and route guidance (RG)[5] effectively and efficiently alleviate freeway congestion and improve traffic safety. The main objectives of this article are to (1) identify the performance of integrated and isolated control in decoupled prediction and simulation environments, and explain control error sources; (2) evaluate the variations in control performance under different combinations of demand scenarios; and (3) investigate control variable profiles from the tested integrated control strategy and explain the integration process and interaction between mainline and on-ramp flows. The applied integrated control of RM and VSL aims to achieve optimal network performance according to traffic states predicted in real time. A METANET-based dynamic traffic model, DynaTAM-RM&VSL (Dynamic Analysis Tool for Active Traffic and Demand Management- Ramp Metering and Variable Speed Limit), was used to perform traffic-state prediction and coordinate mainline and on-ramp flows.

Objective function

Findings

Conclusion and future research