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Safety Benefits of Paved Shoulders in Iowa

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Safety Benefits of Paved Shoulders in Iowa Safety Benefits of Paved Shoulders Updated Final Report August 2010 Area for photos Sponsored by Iowa Department of Transportation (InTrans Project 05-239) About the MTC The Midwest Transportation Consortium (MTC) is a Tier 1 University Transportation Center (UTC) that includes Iowa State University, the University of Iowa, and the University of Northern Iowa. The mission of the UTC program is to advance U.S. technology and expertise in the many disciplines comprising transportation through the mechanisms of education, research, and technology transfer at university-based centers of excellence. Iowa State University, through its Institute for Transportation (InTrans), is the MTC’s lead institution. About CTRE The mission of the Center for Transportation Research and Education (CTRE) at Iowa State University is to develop and implement innovative methods, materials, and technologies for improving transportation efficiency, safety, and reliability while improving the learning environment of students, faculty, and staff in transportation-related fields. Disclaimer Notice The contents of this report reflect the views of the authors, who are responsible for the facts and the accuracy of the information presented herein. The opinions, findings and conclusions expressed in this publication are those of the authors and not necessarily those of the sponsors. The sponsors assume no liability for the contents or use of the information contained in this document. This report does not constitute a standard, specification, or regulation. The sponsors do 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. Non-Discrimination Statement Iowa State University does not discriminate on the basis of race, color, age, religion, national origin, sexual orientation, gender identity, genetic information, sex, marital status, disability, or status as a U.S. veteran. Inquiries can be directed to the Director of Equal Opportunity and Compliance, 3280 Beardshear Hall, (515) 294-7612. Iowa Department of Transportation Statements Federal and state laws prohibit employment and/or public accommodation discrimination on the basis of age, color, creed, disability, gender identity, national origin, pregnancy, race, religion, sex, sexual orientation or veteran’s status. If you believe you have been discriminated against, please contact the Iowa Civil Rights Commission at 800-457-4416 or Iowa Department of Transportation’s affirmative action officer. If you need accommodations because of a disability to access the Iowa Department of Transportation’s services, contact the agency’s affirmative action officer at 800-262-0003. The preparation of this (report, document, etc.) was financed in part through funds provided by the Iowa Department of Transportation through its “Agreement for the Management of Research Conducted by Iowa State University for the Iowa Department of Transportation,” and its amendments. The opinions, findings, and conclusions expressed in this publication are those of the authors and not necessarily those of the Iowa Department of Transportation. Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient’s Catalog No. InTrans Project 05-239 4. Title and Subtitle 5. Report Date Safety Benefits of Paved Shoulders December 2009, Updated August 2010 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. Shauna L. Hallmark, Thomas J. McDonald, Ye Tian, David J. Andersen 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Center for Transportation Research and Education Iowa State University 11. Contract or Grant No. 2711 South Loop Drive, Suite 4700 Ames, IA 50010-8664 12. Sponsoring Organization Name and Address 13. Type of Report and Period Covered Iowa Department of Transportation Updated Final Report 800 Lincoln Way 14. Sponsoring Agency Code Ames, IA 50010 15. Supplementary Notes Visit www.ctre.iastate.edu for color PDF files of this and other research reports. 16. Abstract Single vehicle run-off-road (SVROR) crashes are the largest type of fatal passenger vehicle crash in the US (NCHRP 500 2003). In Iowa, ROR crashes accounted for 36% of rural crashes and 9% of total crashes in 2006. Run-off-road crashes accounted for more than 61.8% of rural fatal crashes and 32.6% of total fatal crashes in Iowa in 2006. The research described in this report evaluates the effectiveness of paved shoulders. Generalized linear models were used to investigate the relationship between crash reduction and implementation of paved shoulders. The response variable was quarterly crash frequency. Separate models were developed for cross-centerline crashes, run-off-road crashes, and single vehicle run-off-road crashes. The model for each independent variable considered over-dispersion and excess zeroes. The best fit model for total crashes per quarter was a zero inflated negative binomial model. Model results indicated that the total amount of right shoulder, presence of a median, speed limit, addition of a paved shoulder and years after addition of a paved shoulder were statistically significant. The effect of paved shoulder varied over time depending on the years after treatment. At 10 years, the decrease is total crashes due to paved shoulders was 15.9%. A negative binominal model was the best fit model for cross-centerline crashes and the model indicated that effect of paved shoulders was not statistically significant. ROR crashes were modeled assuming the distribution of the response variable is a mixture of Poisson and zeros (ZIP). The amount of total right shoulder available, presence of a divided median, speed limit and years after paved shoulders were installed were all statistically significant. The effect of paved shoulder on run-off-road crashes by quarter varied over time depending on the years after treatment. At 10 years, sites with paved shoulders have 13.5% fewer ROR crashes than control sites. Single vehicle run-off-road crashes were modeled assuming the distribution of the response variable is a mixture of Poisson and zeros. The total amount of right shoulder available, presence of a divided median, speed limit and years after paved shoulders were installed were all statistically significant. The effect of paved shoulder on single vehicle run-off-road crashes by quarter varied over time depending on the years after treatment. At 10 years, SVROR crashes are 16.4% lower for sections with paved shoulders than for sites with no treatment. 17. Key Words 18. Distribution Statement paved shoulders—run-off-road crashes No restrictions. 19. Security Classification (of this 20. Security Classification (of this 21. No. of Pages 22. Price report) page) Unclassified. Unclassified. 60 NA Form DOT F 1700.7 (8-72) Reproduction of completed page authorized SAFETY BENEFITS OF PAVED SHOULDERS Updated Final Report December 2009 Updated August 2010 Principal Investigator Shauna L. Hallmark Transportation Engineer Institute for Transportation, Iowa State University Co-Principal Investigator Thomas J. McDonald Safety Circuit Rider Institute for Transportation, Iowa State University Authors Shauna L. Hallmark, Thomas J. McDonald, Yu-Yi Hsu, Ye Tian, David J. Andersen Preparation of this report was financed in part through funds provided by the Iowa Department of Transportation through its research management agreement with the Institute for Transportation, InTrans Project 05-239. A report from Center for Transportation Research and Education Iowa State University 2711 South Loop Drive, Suite 4700 Ames, IA 50010-8664 Phone: 515-294-8103 Fax: 515-294-0467 www.ctre.iastate.edu TABLE OF CONTENTS ACKNOWLEDGMENTS ............................................................................................................ vii EXECUTIVE SUMMARY............................................................................................................ ix 1. INTRODUCTION........................................................................................................................1 1.1 Paved Shoulders .............................................................................................................1 1.2 Rumble Strips ................................................................................................................3 2. DESCRIPTION OF PROJECT ....................................................................................................9 2.1 Project Scope .................................................................................................................9 2.2 Iowa Department of Transportation Current Practices ..................................................9 3. SURVEY OF EXPERT OPINION FIELD MAINTENANCE AND LAW ENFORCEMENT ..............................................................................................................11 3.1 Survey of Field Maintenance Personnel ......................................................................11 3.2 Survey of Law Enforcement ........................................................................................17 4. DATA COLLECTION ...............................................................................................................23 4.1 Identification of Potential Locations ............................................................................23 4.2 Data Collection ............................................................................................................23
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