Experimental Studies for Traffic Incident Management

Brownstone, David; McBride, Michael; Kong, Si-Yuan; Mahmassani, Amine · 2016 · ROSA P / University of California, Irvine.

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Summary

This study addresses the challenge of managing traffic incidents by determining how Variable Message Signs (VMS) can effectively induce drivers to divert from congested freeways to alternate routes. While VMS are widely available, transportation agencies often hesitate to use them for diversion due to fears of overloading surface streets and a lack of understanding regarding how drivers respond to specific message intensities. The research aims to identify VMS messaging schemes that produce predictable and optimal diversion rates, thereby mitigating congestion without causing secondary bottlenecks. To investigate this, the authors conducted a series of laboratory experiments using a 2D real-time driving simulator. Up to 39 subjects per session controlled vehicles on a network consisting of a main freeway and an alternate route with traffic signals. Participants were incentivized with monetary endowments that depreciated over time, creating a controlled value of time. The experiment tested various treatments, including different VMS message types (e.g., incident severity descriptions, lane blockage counts, targeted numeric IDs, and color-coded outlines), dynamic diversion rate recommendations, and road pricing schemes (both dynamic intra-round tolls and static inter-round pricing). Incident scenarios varied in severity, from no impediment to complete lane blockages, requiring drivers to make route choices before congestion became visible. The results indicate that the content and targeting of VMS messages significantly influence driver behavior and aggregate network performance. Treatments involving targeted messaging, such as public color outlines or numeric IDs that instructed specific drivers to divert, generally yielded higher compliance and more optimal traffic distributions compared to generic informational messages. Dynamic diversion rate messages, which updated the recommended proportion of drivers to exit based on real-time conditions, also performed well in nudging subjects toward optimal route allocation. Conversely, generic messages describing incident severity often led to unpredictable diversion rates, sometimes resulting in over-diversion. Road pricing schemes, particularly dynamic intra-round pricing, effectively adjusted route choices by altering the financial incentive, though responses varied depending on whether value of time was homogeneous or heterogeneous among subjects. The significance of this work lies in providing empirical evidence for optimizing VMS strategies in traffic incident management. The findings suggest that system operators can achieve desired diversion rates by using targeted, dynamic, or pricing-based interventions rather than relying solely on static, generic information. This approach helps mitigate the risk of over-diversion and improves overall network efficiency. The study contributes to the field by demonstrating that specific manipulations of VMS content can reliably control aggregate driver behavior, offering a practical framework for improving real-time traffic management systems.

Key finding

Targeted messaging schemes using public color outlines to identify specific vehicles achieved diversion rates closest to the system-optimal level compared to qualitative descriptions or static diversion rate targets.

Methodology

simulator

Sample size: 39

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

Topics

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• traffic density

Information type

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• Applied Guidance: countermeasure evaluation