Improving Travel Time Reliability with Variable Speed Limits

TL;DR

This paper proposes two models using variable speed limits to improve travel time reliability on bottleneck corridors, considering stochastic demand and capacity, validated with real data.

Contribution

It introduces two novel models for setting variable speed limits that optimize travel time reliability under stochastic demand and capacity conditions.

Findings

Both models effectively improve travel time reliability.

Numerical examples demonstrate practical applicability with real data.

Models outperform fixed speed limit strategies.

Abstract

This paper analyzes the use of variable speed limits to optimize travel time reliability for commuters. The investigation focuses on a traffic corridor with a bottleneck subject to the capacity drop phenomenon. The optimization criterion is a linear combination of the expected value and standard deviation of average travel time, with traffic flow dynamics following the kinematic wave model (Lighthill, 1955; Richards, 1956). We develop two complementary models to optimally set variable speed limits: In the first model, daily peak traffic demand is conceptualized as a stochastic variable, and the resulting model is solved through a three-stage optimization algorithm. The second model is based on deterministic demand, instead modeling bottleneck capacity as a stochastic process using a stochastic differential equation (SDE). The practical applicability of both approaches is demonstrated through numerical examples with empirically calibrated data.