Evaluation of Dynamic Speed Feedback Signs on Curves: A National Demonstration Project

Hallmark, Shauna; Hawkins, Neal; Smadi, Omar · 2015 · ROSA P / United States. Federal Highway Administration

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Summary

This report evaluates the effectiveness of Dynamic Speed Feedback Signs (DSFS) in reducing vehicle speeds and crash risks on rural horizontal curves. The study was motivated by the high prevalence of speeding-related fatalities, particularly on non-interstate local streets and collector roads where lane departure crashes are frequent. The primary objective was to determine whether DSFS systems, which alert drivers to roadway conditions and provide recommended speeds, could serve as an effective tool for speed management and crash mitigation. The research was conducted as a national demonstration project by the Center for Transportation Research and Education at Iowa State University, sponsored by the Federal Highway Administration. The study utilized a before-and-after experimental design across 22 sites on rural two-lane roadways in seven states: Arizona, Florida, Iowa, Ohio, Oregon, Texas, and Washington. Two types of DSFS were evaluated. Data collection occurred prior to installation and at one, 12, and 24 months post-installation. The analysis focused on speed metrics, including mean speed, 85th percentile speed, and the percentage of vehicles exceeding posted or advisory speed limits by specific margins (5, 10, 15, and 20 mph). Additionally, a crash analysis was performed using a Full Bayes model to develop Crash Modification Factors (CMFs). The results indicated that DSFS were effective in reducing speeds. At the point of curvature (PC), most sites experienced decreases in mean speed, with reductions up to 10.9 mph observed at both the PC and the center of the curve (CC). Most sites saw a decrease in 85th percentile speed of 3 mph or more at the PC and 2 mph at the CC. Furthermore, there were large reductions in the number of vehicles traveling significantly over the posted or advisory speed limits across all post-installation periods. The crash analysis yielded CMFs ranging from 0.93 to 0.95, depending on crash type and direction, suggesting a modest reduction in crash frequency. The study concludes that DSFS are a viable, low-cost safety improvement for managing speeds on rural horizontal curves. By effectively reducing both average and high-end speeds, these signs contribute to lowering the risk of lane departure crashes. The findings provide traffic safety engineers with empirical evidence and specific CMFs to support the implementation of DSFS as part of broader speed management strategies. The report emphasizes that while the speed reductions were significant, the crash reduction benefits, while positive, were more modest, highlighting the need for continued evaluation and potentially complementary safety treatments.

Key finding

Dynamic speed feedback signs reduced mean speeds by up to 10.9 mph at the point of curvature and produced crash modification factors between 0.93 and 0.95.

Methodology

field_study

Sample size: 22

Provenance

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

Topics

Ranked by relevance to this paper. Hover a topic for its definition.

• speed management
• speed choice
• perceptual countermeasures
• signage environment

Information type

What kind of knowledge this paper contributes, grouped by family — independent of topic (what it is about) and method (how it was studied).

• Applied Guidance: countermeasure evaluation
• Empirical Findings: crash risk outcomes