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  • Cooperative Research Program

    TTI: 0-6932

    Technical Report 0-6932-R1

    Pavement Safety-Based Guidelines for Horizontal Curve Safety

    in cooperation with the Federal Highway Administration and the

    Texas Department of Transportation http://tti.tamu.edu/documents/0-6932-R1.pdf

    TEXAS A&M TRANSPORTATION INSTITUTE

    COLLEGE STATION, TEXAS

  • Technical Report Documentation Page 1. Report No. FHWA/TX-18/0-6932-R1

    2. Government Accession No. 3. Recipient's Catalog No.

    4. Title and Subtitle PAVEMENT SAFETY-BASED GUIDELINES FOR HORIZONTAL CURVE SAFETY

    5. Report Date Published: November 2018 6. Performing Organization Code

    7. Author(s) Michael P. Pratt, Srinivas R. Geedipally, Bryan Wilson, Subasish Das, Marcus Brewer, and Dominique Lord

    8. Performing Organization Report No. Report 0-6932-R1

    9. Performing Organization Name and Address Texas A&M Transportation Institute College Station, Texas 77843-3135

    10. Work Unit No. (TRAIS)

    11. Contract or Grant No. Project 0-6932 -

    12. Sponsoring Agency Name and Address Texas Department of Transportation Research and Technology Implementation Office 125 E. 11th Street Austin, Texas 78701-2483

    13. Type of Report and Period Covered Technical Report: September 2016–August 2018 14. Sponsoring Agency Code

    15. Supplementary Notes Project performed in cooperation with the Texas Department of Transportation and the Federal Highway Administration. Project Title: Developing Pavement Safety-Based Guidelines for Improving Horizontal Curve Safety URL: http://tti.tamu.edu/documents/0-6932-R1.pdf 16. Abstract

    The Texas Department of Transportation is increasing its efforts to improve rural highway curve safety by including high-friction surface treatments in the Highway Safety Improvement Program (HSIP). A handful of efforts are underway in the state to install these treatments or others that are intended to improve safety by increasing pavement skid resistance. However, HSIP funds are very limited. Hence, it is necessary to prioritize projects carefully to spend the limited funds where they would yield the greatest benefit in terms of crashes reduced and injuries and fatalities prevented.

    Documents like the Roadway Safety Design Workbook and the Highway Safety Manual contain much useful information about the safety effects of design characteristics like curve radius and cross-sectional widths, but pavement characteristics are not yet included in these documents. In this research project, researchers calibrated detailed safety prediction models to account for the effects of key curve characteristics, including geometry, pavement variables (particularly skid resistance), and weather patterns. Additionally, researchers developed estimates of the service life for various surface treatments that may be used to increase skid resistance. By combining safety prediction models, weather data, and service life data, researchers created guidelines and a life-cycle benefit-cost evaluation framework to assist practitioners in choosing effective safety treatments for curves. 17. Key Words Highway Design, Highway Safety, Rural Highways, Highway Curves, Pavement, Skid Resistance, Crash, Crash Risk

    18. Distribution Statement No restrictions. This document is available to the public through NTIS: National Technical Information Service Alexandria, Virginia 22312 http://www.ntis.gov

    19. Security Classif. (of this report) Unclassified

    20. Security Classif. (of this page) Unclassified

    21. No. of Pages 174

    22. Price

    Form DOT F 1700.7 (8-72) Reproduction of completed page authorized

    http://tti.tamu.edu/documents/0-6932-R1.pdf http://www.ntis.gov/

  • PAVEMENT SAFETY-BASED GUIDELINES FOR HORIZONTAL CURVE SAFETY

    by

    Michael P. Pratt, P.E. Assistant Research Engineer

    Srinivas R. Geedipally, Ph.D., P.E.

    Associate Research Engineer

    Bryan Wilson, P.E. Associate Research Scientist

    Subasish Das, Ph.D.

    Associate Transportation Researcher

    Marcus Brewer, P.E. Associate Research Engineer

    Texas A&M Transportation Institute

    and

    Dominique Lord, Ph.D.

    Professor

    Texas A&M University

    Report 0-6932-R1 Project 0-6932

    Project Title: Developing Pavement Safety-Based Guidelines for Improving Horizontal Curve Safety

    Performed in cooperation with the Texas Department of Transportation

    and the Federal Highway Administration

    Published: November 2018

    TEXAS A&M TRANSPORTATION INSTITUTE College Station, Texas 77843-3135

  • v

    DISCLAIMER The contents of this report reflect the views of the authors, who are responsible for the facts and the accuracy of the data published herein. The contents do not necessarily reflect the official view or policies of the Federal Highway Administration (FHWA) and/or the Texas Department of Transportation (TxDOT). This report does not constitute a standard, specification, or regulation. It is not intended for construction, bidding, or permitting purposes. The engineer in charge of the project was Michael P. Pratt, P.E. #102332.

    NOTICE

    The United States Government and the State of Texas do not endorse products or manufacturers. Trade or manufacturers’ names appear herein solely because they are considered essential to the object of this report.

  • vi

    ACKNOWLEDGMENTS TxDOT and FHWA sponsored this research project. Mr. Michael Pratt, Dr. Srinivas Geedipally, Mr. Bryan Wilson, Dr. Subasish Das, and Mr. Marcus Brewer with the Texas A&M Transportation Institute, and Dr. Dominique Lord with Texas A&M University prepared this report. The researchers acknowledge the support and guidance that the project monitoring committee provided:

    • Mr. Darrin Jensen, Project Manager (TxDOT, Research and Technology Implementation Office).

    • Mr. Tommy Abrego (TxDOT, Policy and Standards). • Mr. Epigmenio Gonzalez (TxDOT, Pharr District). • Mr. John Bassett (TxDOT, Construction Division). • Mr. Soojun Ha (TxDOT, Houston District). • Ms. Patti Dathe, Contract Specialist (TxDOT, Research and Technology Implementation

    Office). In addition, the researchers acknowledge the valuable contributions of Mr. Tom Freeman, Mr. Yash Menaria, Mr. Soheil Sohrabi, Ms. Ruth Iroanya, Mr. Pawan Dixit, and Ms. Katherine Lufkin, who assisted with various tasks during the conduct of the project.

  • vii

    TABLE OF CONTENTS

    List of Figures ............................................................................................................................... ix List of Tables ................................................................................................................................ xi Chapter 1: Overview..................................................................................................................... 1

    Introduction ................................................................................................................................. 1 Research Approach ..................................................................................................................... 1

    Chapter 2: State of the Practice: Curve Crash Trends and Pavement Management Practices ......................................................................................................................................... 3

    Introduction ................................................................................................................................. 3 Curve Safety Performance and Crash Trends ............................................................................. 3

    Curve Geometry ...................................................................................................................... 4 Curve Traffic Control Devices ................................................................................................ 8 Weather ................................................................................................................................... 9

    Effectiveness and Service Life of Surface Treatments ............................................................. 10 Treatment Descriptions ......................................................................................................... 11 Treatment Performance and Cost .......................................................................................... 15 Summary of Treatment Safety Effectiveness ....................................................................... 17 Influence of Pavement Variables on Crash Frequency ......................................................... 17 Comparison of Skid Number CMFs ..................................................................................... 23

    State Agency Practices .............................................................................................................. 25 Survey Questions .................................................................................................................. 25 Survey Responses ................................................................................................................. 28

    Other Issues ............................................................................................................................... 30 Design Considerations