70 Mph Study
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70 mph Study FINAL REPORT June 30, 2016 By Eric T. Donnell, Bachir Hamadeh, Lingyu Li, and Jonathan Wood The Thomas D. Larson Pennsylvania Transportation Institute COMMONWEALTH OF PENNSYLVANIA DEPARTMENT OF TRANSPORTATION CONTRACT # 4400008014 WORK ORDER # PSU 013 Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient’s Catalog No. FHWA-PA-2016-009-PSU WO 13 4. Title and Subtitle 5. Report Date June 30, 2016 70mph Study 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. Eric T. Donnell, Bachir Hamadeh, Lingyu Li, and Jonathan S. Wood LTI 2016-26 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) The Thomas D. Larson Pennsylvania Transportation Institute The Pennsylvania State University 11. Contract or Grant No. 201 Transportation Research Building University Park, PA 16802 4400008014, PSU WO 13 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered The Pennsylvania Department of Transportation Final Report: 12/4/14 – 6/30/16 Bureau of Planning and Research Commonwealth Keystone Building 400 North Street, 6th Floor 14. Sponsoring Agency Code Harrisburg, PA 17120-0064 15. Supplementary Notes COTR: Robert Pento, Manager, Traffic Engineering and Permits, Pennsylvania Department of Transportation, Phone: (717) 783- 6265, E-mail: [email protected] 16. Abstract In July and August 2014, the Pennsylvania Department of Transportation (PennDOT) and Pennsylvania Turnpike Commission (PTC) raised the posted speed limit on rural sections of Interstates 80, 380, and 76 from 65 to 70 mph. The purpose of this study was to assess the speed and safety performance of these “pilot” sections. This was done by comparing the operating speeds and crash frequencies before and after the posted speed limit increase. Additionally, operating speed data in several work zones were collected to assess how drivers comply with posted speed limits in work zones on the pilot sections. An inferred design speed method and pavement friction degradation method are proposed as methodologies to assess site conditions on rural Interstate roadways with 65 mph posted speed limits. Collectively, the operating speed, safety, inferred design speed, and friction information can be used by PennDOT and the PTC to identify candidate locations for 70 mph posted speed limits. The findings suggest that mean and 85th-percentile operating speeds increased after increasing the posted speed limit from 65 to 70 mph; however, the increases were less than 5 mph. A framework was developed to estimate the safety effects of the posted speed limit increase, because only 12 to 16 months of after period crash data were available for the analyses included in this study. 17. Key Words 18. Distribution Statement No restrictions. This document is available Speed limits, safety, operating speed, inferred design speed, pavement from the National Technical Information Service, friction, work zones Springfield, VA 22161 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price N/A Unclassified Unclassified 145 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized Disclaimer This work was sponsored by the Pennsylvania Department of Transportation and the U.S. Department of Transportation, Federal Highway Administration. The contents of this report reflect the views of the authors, who are responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of either the Federal Highway Administration, U.S. Department of Transportation, or the Commonwealth of Pennsylvania at the time of publication. This report does not constitute a standard, specification, or regulation. Acknowledgement The authors wish to acknowledge Mr. Glenn Rowe, Chief, PennDOT Traffic Engineering and Permits, for initiating this project. The authors are grateful for the technical support and guidance of Mr. Robert Pento, Manager of Traffic Engineering and Permits at PennDOT, during the project. Ms. Heather Heslop, PennDOT Research Program Manager, is acknowledged for her support. The research team also received guidance and assistance from several staff members of the Pennsylvania Turnpike Commission. Mr. Thomas Macchione, Manager of Traffic Engineering, coordinated this effort and provided helpful guidance and support during the project. Finally, the authors wish to acknowledge Messrs. Keith Johnson and Mark Unger from AECOM for answering questions about the data supplied by the Pennsylvania Turnpike Commission, and for offering comments on several project deliverables. TABLE OF CONTENTS List of Tables .............................................................................................................................................................. v List of Figures ........................................................................................................................................................... vii Introduction ................................................................................................................................................................. 1 Background ................................................................................................................................................................. 2 Speed and Road Safety .............................................................................................................................................. 3 Literature Review ..................................................................................................................................................... 11 Effect of Posted Speed Limit Changes on Driving Speeds....................................................... 11 Effect of Lowering Posted Speed Limits on Driving Speeds ............................................... 11 Effects of Posted Speed Limit Increases on Driving Speeds ................................................ 12 Relationship between Changing Speed Limits and Crash Frequency and Severity ................. 17 Reducing Posted Speed Limits ............................................................................................. 17 Increasing Posted Speed Limits ............................................................................................ 19 Work Zone Speed Limits .......................................................................................................... 27 State Transportation Agency Practices Related To Increasing Posted Speed Limits ............... 29 Idaho ..................................................................................................................................... 29 Texas ..................................................................................................................................... 29 Wyoming............................................................................................................................... 31 Ohio....................................................................................................................................... 31 New Hampshire .................................................................................................................... 32 Michigan ............................................................................................................................... 34 Overview of Evaluations ......................................................................................................................................... 35 Operating Speed and Speed Limit Compliance Assessment .............................................................................. 37 Data Collection Procedures ....................................................................................................... 37 Statistical Analysis .................................................................................................................... 41 Analysis Results ........................................................................................................................ 44 PennDOT Interstates 80 and 380 .......................................................................................... 44 Pennsylvania Turnpike Interstate 76 (Non-Work Zones) ..................................................... 49 Pennsylvania Turnpike Interstate 76 (Work Zones) ............................................................. 53 Speeds Approaching and Departing 70 mph Speed Limit Zones ......................................... 56 Speeds Approaching and Departing Work Zone in 70 mph Speed Limit Zones.................. 58 iii Safety Evaluation ..................................................................................................................................................... 59 Before-After Crash Rate Evaluation ......................................................................................... 59 Safety Performance Functions .................................................................................................. 64 Pavement Friction Assessment ............................................................................................................................... 68 Pennsylvania Turnpike.............................................................................................................. 68 Friction Degradation Model .................................................................................................