A Comparative Study between Vehicle Activated Signs and Speed Indicator Devices

Jomaa, Diala; Yella, Siril; Dougherty, Mark · 2017 · OpenAlex-citations

DOI: 10.1016/j.trpro.2017.03.017

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Summary

This study investigates the comparative effectiveness of Vehicle Activated Signs (VAS) and Speed Indicator Devices (SID) in reducing vehicle speeds and speed variability. While both signs warn drivers exceeding a threshold speed, VAS displays a static warning message, whereas SID shows the driver’s current speed in green or red. The research aims to determine the most suitable signage for specific contexts by analyzing the impact of site type (local roads vs. highways), time of day, and trigger speed settings on driver behavior. The experimental design utilized two test sites in Borlänge, Sweden: Mjälga, a local road with a 40 km/h limit, and Djurås, a highway segment with a 60 km/h limit. Data were collected using Doppler radars positioned 100 meters before and at the sign location over two one-week periods: a baseline period without signs and an intervention period with signs installed sequentially. A total of 5,488 observations were recorded. Trigger speeds were set to either the posted speed limit or the 85th percentile speed. The study measured the "detectable effect" on mean speed and the coefficient of variation to assess speed dispersion. Statistical significance was evaluated using two-way Analysis of Variance (ANOVA). Results indicated that both signs significantly reduced mean speeds and standard deviations. However, their effectiveness varied by context. On local roads (Mjälga), SID was more effective than VAS in reducing mean speed. On highways (Djurås), the effectiveness of both signs was comparable. Regarding trigger speeds, ANOVA revealed that the trigger speed setting significantly affected driver response for VAS but not for SID. Specifically, setting the VAS trigger speed to the 85th percentile significantly lowered the coefficient of variation, particularly during daytime hours. In contrast, SID’s impact on mean speed remained consistent regardless of whether the trigger was set to the speed limit or the 85th percentile. The time of day and site type were statistically significant factors for both signs, though no interaction was found between trigger speed and these factors for SID. The study concludes that SID is generally more effective on local roads and requires less tuning, as its efficacy is independent of trigger speed settings. VAS, however, benefits from optimization, with the 85th percentile speed serving as an effective trigger to minimize speed variance. For highways, both signs perform similarly, suggesting that selection may depend on other factors like cost. The findings imply that traffic authorities should consider site characteristics and operational simplicity when choosing between these safety devices, with SID offering a robust solution for local areas and VAS requiring careful calibration for optimal performance.

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Topics

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• signage environment
• speed management
• perceptual countermeasures