Federal Highway Administration University Course on Bicycle and Pedestrian Transportation: Lesson 20: Traffic Calming

NHTSA · 2006 · ROSA P / United States. Department of Transportation. Federal Highway Administration

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Summary

This document, Lesson 20 of the Federal Highway Administration’s University Course on Bicycle and Pedestrian Transportation, addresses the principles, design, and implementation of traffic calming measures. The primary objective is to reduce vehicle speed and volume to levels appropriate for specific street functional classes and adjacent land uses, thereby improving safety for pedestrians and bicyclists, reducing noise, and enhancing neighborhood livability. The text emphasizes that traffic calming should address the root causes of traffic problems rather than merely treating symptoms, and it stresses the necessity of consulting emergency services early to ensure response times are not compromised. The lesson categorizes traffic-calming devices into six groups: bumps and humps, reduced street areas, street closures, traffic diversions, surface texture/visual devices, and parking treatments. It provides detailed design specifications for each category. For raised pavement areas, such as speed humps and tables, the text outlines dimensions, spacing (typically 91–183 meters), and considerations for bicycle accessibility, including the use of cycle slips. For street narrowing techniques like slow points, medians, and curb extensions, the document highlights the need to balance speed reduction with adequate space for bicyclists to avoid being squeezed by motorists. Specific recommendations include maintaining minimum lane widths of 3.5 meters for safe passing and using textured surfaces to signal speed changes. The text also covers street closures and diverters, noting that while they effectively eliminate through-traffic, they can inconvenience residents and require careful design to maintain emergency access and bicycle continuity. Evidence-based findings are presented through case studies and comparative data. A before-and-after study of speed humps in Bellevue, Washington, demonstrated significant reductions in the 85th percentile speed across various residential street types, though daily traffic volumes sometimes increased or remained stable depending on alternative route availability. The document also compares roundabouts to signalized intersections, citing lower crash rates for roundabouts. Conversely, it notes that diagonal diverters in Seattle increased travel times and confused users, leading to a shift toward traffic circles. The text warns that isolated measures often have limited effectiveness; for instance, medians alone do not significantly reduce speeds unless combined with other devices. The significance of this work lies in its comprehensive guidance for practitioners on selecting and combining traffic-calming strategies to achieve specific safety and operational goals. It underscores that successful implementation requires a holistic approach, considering the entire street network, emergency access, and the needs of non-motorized users. By providing specific design parameters and highlighting common pitfalls, such as ignoring the source of traffic problems or creating hazards for cyclists, the lesson serves as a practical toolkit for engineers and planners aiming to create safer, more livable urban environments.

Key finding

Traffic calming is defined as a combination of mainly physical measures that reduce the negative effects of motor vehicle use, alter driver behavior, and improve conditions for nonmotorized street users.

Methodology

review

Provenance

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Topics

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• speed management
• perceptual countermeasures