Selection of the Speed Command Distance for Improved Performance of a Rule-Based VSL and Lane Change Control

TL;DR

This paper investigates how the distance of Variable Speed Limit (VSL) signs from bottlenecks affects traffic flow and safety, proposing a rule-based control strategy and analytical bounds to optimize VSL placement for improved system performance.

Contribution

It introduces a novel analysis of VSL sign placement impact, proposing a control strategy and deriving bounds to enhance traffic management effectiveness.

Findings

The VSL sign distance significantly influences traffic flow and safety.

A lower bound for VSL zone distance guarantees homogeneous traffic density.

Simulation results confirm improved mobility, safety, and emissions when using the proposed bounds.

Abstract

Variable Speed Limit (VSL) control has been one of the most popular techniques with the potential of smoothing traffic flow, maximizing throughput at bottlenecks, and improving mobility and safety. Despite the substantial research efforts in the application of VSL control, few studies have looked into the effect of the VSL sign distance from the point of an accident or a bottleneck. In this paper, we show that this distance has a significant impact on the effectiveness and performance of VSL control. We propose a rule-based VSL strategy that matches the outflow of the upstream VSL zone with the bottleneck capacity based on a multi-section Cell Transmission Model (CTM). Then, we consider the distance of the upstream VSL zone as a control variable and perform a comprehensive analysis of its impact on the performance of the closed-loop traffic control system based on the multi-section CTM. We develop a lower bound that this distance needs to satisfy in order to guarantee homogeneous traffic density across sections and reduce bottleneck congestion. The bound is verified analytically and demonstrated using microscopic simulation of traffic on I-710 in Southern California. The simulations are used to quantify the benefits on mobility, safety and emissions obtained by selecting the upstream VSL zone distance to satisfy the analytical lower bound. The developed lower bound is a design tool which can be used to tune and improve the performance of VSL controllers.