Variable Message Sign strategies for Congestion Warning on Motorways

Alhajyaseen, Wael Khaleel Mohammad; Reinolsmann, Nora; Brijs, Kris; Brijs, Tom · 2018 · Crossref

DOI: 10.5339/qfarc.2018.ictpd260

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Summary

This study investigates the effectiveness of Variable Message Sign (VMS) strategies for warning drivers about congestion on motorways, aiming to reduce rear-end collisions associated with hard congestion tails. Despite motorways being designed as safe environments, they account for significant fatalities in the European Union, particularly due to sudden stops caused by congestion. While VMS are a key component of Intelligent Transportation Systems intended to help drivers anticipate traffic events, existing guidelines offer inconsistent findings regarding sign design, message content, and placement. The research specifically addresses the need for empirical evidence on how different VMS formats influence driver behavior and safety performance. To evaluate these factors, the researchers employed a driving simulator study involving thirty-six participants with an average age of 43. The experiment utilized a within-subject design where all participants were exposed to seven randomized VMS scenarios. The simulation apparatus was a medium-fidelity fixed-base simulator featuring a Ford Mondeo mock-up and a 180° visual environment. Data collection included driving parameters such as speed, deceleration, and accident occurrence, as well as eye-tracking data recorded via a FaceLAB 5.0 system to monitor gaze fixations and visual load. The study focused on gantry-mounted and cantilever-mounted signs with varying message formats, including pictograms, text units, and distance information, placed at different distances prior to the congestion tail. The results indicated that driver initial speed significantly influenced stopping distance and crash likelihood, with higher speeds leading to closer stops and increased rear-end collision risk. The most effective strategy was a gantry-mounted VMS displaying a pictogram and the word “congestion” located 1 km before the congestion tail. This configuration resulted in the lowest mean speeds and the smoothest deceleration profiles for all drivers. In contrast, warnings placed more than 3 km ahead had no significant effect on driver behavior in the critical zone, as drivers tended to accelerate again before reaching the congestion. Additionally, gantry-mounted signs elicited more frequent but shorter eye fixations compared to cantilevers, and increasing the number of information units on the VMS increased the visual load on drivers. The study concludes that the distance between the warning sign and the congestion tail is a critical determinant of VMS effectiveness. Warnings placed too far away lose their impact in the critical approach zone, while those placed too close may compromise safe deceleration. The optimal configuration identified was a gantry-mounted sign with a pictogram and text at a 1 km distance, which was clearly visible from all lanes without imposing excessive visual load. These findings suggest that precise placement and simplified message design are essential for maximizing the safety benefits of congestion warnings, providing specific guidance for improving VMS harmonization and implementation in Intelligent Transportation Systems.

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Topics

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• signage environment
• traffic density
• emergency work zone conspicuity
• perceptual countermeasures