Guide to Vertical Deflection Speed Reduction Techniques

New ITE Recommended Practice Adopted

Availability

The final version of A Guide to Vertical Deflection Speed Reduction Techniques: Planning and Design of Speed Humps, Speed Tables and Other Related Measures (RP-038C) was adopted by the Institute of Transportation Engineers (ITE) International Board of Direction in December 2022.

In response to the comments received on the proposed version of the document, the report has been revised as follows:

• Title changed to emphasize that the recommended practice focuses on vertical deflection design elements as speed reduction techniques;
• Discussion added on speed cushion versus traverse speed hump design;
• Supplemental information included from other countries;
• Discussion of speed and devices’ impact on speed updated;
• Context and design for pedestrian, bicycle and transit vehicles supplemented;
• Definitions updated and consistent use of terms reviewed throughout; and
• Figures and tables revised as well as other technical and editorial revisions to improve readability and clarity.

The report is now available in the ITE Bookstore at this link.

Description

Vertical deflection measures as a traffic calming speed reduction technique include speed humps, speed tables, raised pedestrian crossings, raised intersections and fully mountable mini-roundabouts. While the prior RP focused on speed humps and speed tables, the proposed RP expands the discussion to be more inclusive of intersection as well as mid-block techniques. Over the past decade as more measures have been installed and more data regarding effectiveness (positive or negative) have been collected, refinements have emerged, including:

• Replacing transverse humps with a cushion design to better address all road users
• Greater understanding of what a speeding and volume problem is quantitatively
• Defining safety related speed metrics such as excessive speeding and racing (percentages of vehicles traveling 5 and 10 mph above proper speed limits)
• Improved data collection of speed distribution to include 2 mph bins
• Uniform pavement markings
• More before and after study data regarding understanding of performance relative to speed and volume
• Documentation of legal case studies and issues of liability
• Understanding of property value, noise, air quality, pavement impact and wheelbase of vehicles

This proposed recommended practice was written primarily for engineers and planners working for public agencies to guide planning, public engagement and applications of speed reduction techniques. It’s primary audience will be agencies and roadway owners in the United States for two reasons. First, there is renewed interest in self-enforcing speed limits in the recently released National Road Safety Strategy and second, no national speed hump guidelines exist. Canada, Australia, New Zealand, United Kingdom and other countries have national guidelines. A comparison is provided to these guidelines with this RP. While the majority of findings from the prior recommended practice remain unchanged (many of the design items for example), refinements to planning issues, public engagement, studies and implementation practices have been made. A brief new section is provided on options to hump such as vehicle speed feedback signs which accomplish comparable results at similar costs (before/after data is shared). An introduction to practices in Australia/New Zealand where speed tables are being utilized on higher speed roads (35 mph) is mentioned but until further research is completed in this area, this RP does not address guidance for such measures at this time. The format includes numerous common questions to guide analysts in their understanding of the context and characteristics of where speed reduction techniques are appropriate for users. These can be used to:

• Better inform citizens of value, impacts and the full range of considerations
• Develop a fair, transparent, clear, well-defined and legally defensible program
• Guide planning, study, design, implementation, inspection and maintenance
• Build greater familiarity with best practices

Development

This guide is the result of concerted effort by dedicated volunteers which started in the spring of 2021 under the oversight of the Traffic Engineering Council. ITE wishes to thank both the task force and ITE headquarter staff for their role in completing this task. The recommended practice has been balloted and approved by a separate review panel of individuals with background in traffic calming and roadway safety.