September 2009
FHWA-SA-10-001
FOREWORD
The speed at which drivers operate their vehicles directly affects two performance measures of the highway system—mobility and safety. Higher speeds provide for lower travel times, a measure of good mobility. However, the relationship of speed to safety is not as clear cut. It is difficult to separate speed from other characteristics including the type of highway facility. Still, it is generally agreed that the risk of injuries and fatalities increases with speed. Designers of highways use a designated design speed to establish design features; operators set speed limits deemed safe for the particular type of road; but drivers select their speed based on their individual perception of safety. Quite frequently, these speed measures are not compatible and their values relative to each other can vary. This guide discusses the various speed concepts to include designated design speed, operating speed, speed limit, and a new concept of inferred design speed. It explains how they are determined and how they relate to each other.
The purpose of this publication is to help engineers, planners, and elected officials to better understand design speed and its implications in achieving desired operating speeds and setting rational speed limits.
Joseph S. Toole
Associate Administrator,
Office of Safety,
Federal Highway Administration
Notice
This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document. This report does not constitute a standard, specification, or regulation.
The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers’ names appear in this report only because they are considered essential to the objective of the document.
Quality Assurance Statement
The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.
Technical Documentation Page
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1. Report No. FHWA FHWA-SA-10-001 |
2. Government Accession No. |
3. Recipient's Catalog No. |
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4. Title and Subtitle Speed Concepts: Informational Guide |
5. Report Date December 2009 |
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6. Performing Organization Code
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7. Authors Eric T. Donnell, Ph.D., P.E; Scott C. Hines, Kevin M. Mahoney, D. Eng., P.E., Richard J. Porter, Ph.D., Hugh McGee, Ph.D., P.E. |
8. Performing Organization Report No. |
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9. Performing Organization Name and Address Thomas D. Larson Pennsylvania Transportation Institute Vanasse Hangen Brustlin, Inc. |
10. Work Unit No.
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11. Contract or Grant No. DTFH61-03-D-00105 |
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12. Sponsoring Agency Name and Address Office of Safety |
13. Type of Report and Period Covered Report |
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14. Sponsoring Agency Code
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15. Supplementary Notes: FHWA COTR: Edward Sheldahl, Office of Safety. |
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16. Abstract Traffic speed is an important yet complex topic in the transportation engineering community. Furthermore, speed is of considerable interest to enforcement agencies, safety advocates, property owners, users of the transportation system, and the public at-large because of its perceived effect on crash risk. Each of these stakeholders perceives speed measures differently; therefore, many issues related to speed are either misunderstood or remain unanswered. The objectives of this guide is to:
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17. Key Words Traffic speed, design speed, inferred design speed, operating speed |
18. Distribution Statement
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19. Security Classif. (of this report) Unclassified |
20. Security Classif. (of this page) Unclassified |
21. No. of Pages: 59 |
22. Price |
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Form DOT F 1700.7 (8-72) - Reproduction of completed pages authorized