Factors Contributing to Median Encroachments and Cross-Median Crashes (2014)

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N A T I O N A L C O O P E R A T I V E H I G H W A Y R E S E A R C H P R O G R A M NCHRP REPORT 790 Factors Contributing to Median Encroachments and Cross-Median Crashes Douglas W. Harwood, David K. Gilmore, Jerry L. Graham, and Mitchell K. O’Laughlin MRIGlobal Kansas City, MO Alison M. Smiley and Thomas P. Smahel HuMan FactoRs noRtH Toronto, ON, Canada Subscriber Categories Design • Safety and Human Factors TRANSPORTAT ION RESEARCH BOARD WASHINGTON, D.C. 2014 www.TRB.org Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration

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C O O P E R A T I V E R E S E A R C H P R O G R A M S CRP STAFF FOR NCHRP REPORT 790 Christopher W. Jenks, Director, Cooperative Research Programs Christopher Hedges, Manager, National Cooperative Highway Research Program B. Ray Derr, Senior Program Officer Andrea Parker, Senior Program Assistant Eileen P. Delaney, Director of Publications Hilary Freer, Senior Editor NCHRP PROJECT 17-44 PANEL Field of Traffic—Area of Safety Howard R. Ressel, New York State DOT, Rochester, NY (Chair) David K. Olson, Rochester, WA James A. Barna, Ohio DOT, Columbus, OH Rick O. Drumm, Federal Highway Administration, Indianapolis, IN Erik O. Emerson, Wisconsin DOT, Madison, WI Young-Jun Kweon, Virginia DOT, Charlottesville, VA Xiaokun “Cara” Wang, Rensselaer Polytechnic Institute, Troy, NY J. Richard Young, Jr., Atkins North America, Inc., Jackson, MS Nicholas A. Artimovich, II, FHWA Liaison Stephen F. Maher, TRB Liaison

F O R E W O R D By B. Ray Derr Staff Officer Transportation Research Board This report identifies design and operational factors that contribute to the frequency and severity of median encroachments and cross-median crashes. It also identifies counter- measures for addressing those contributory factors. The report will be useful to designers and safety professionals in reducing these highly visible crashes. Cross-median crashes frequently result in high-severity injuries and fatalities. Previous studies of contributory factors associated with cross-median crashes have typically focused on median width and average daily traffic (ADT). A few studies have looked at the influence of geometry and cross-sectional elements. Although these studies have been helpful, they did not explore many other design and operational factors that may contribute to cross- median crash frequency or severity (e.g., interchange ramps, interchange spacing, mix- ture of vehicle types, peak-period volumes, peak-period duration, land use, access control, driver workload, posted speed, or presence of speed transition zones). All median-related incidents begin with a median encroachment. Reducing median encroachments will reduce both cross-median crashes and fixed-object crashes in the median. Consequently, analyzing median encroachments should provide additional insight into the causes of cross-median crashes. There is also a knowledge gap regarding countermeasures appropriate for the various fac- tors contributing to median encroachments and cross-median crashes. Although installing a barrier will greatly reduce cross-median crashes, it will also increase fixed-object crashes and the crash risk of maintenance personnel. Other countermeasures besides barriers exist, and knowing which ones effectively address the contributory factors on a highway will allow an engineer to develop a more effective design. In NCHRP Project 17-44, MRIGlobal reviewed the literature on median encroachments and cross-median crashes. Based on a survey of states, Canadian provinces, and turnpike/toll road authorities, the team compiled a list of design and operational factors likely to contribute to median encroachments and cross-median crashes. The research team then collected data to determine the relative contribution of each of the factors to median encroachments and cross-median crashes. Appendix D of the report provides recommended guidelines for reducing the frequency and severity of median-related crashes. This material is designed to be easily incorporated into a transportation agency’s design manual.

C O N T E N T S 1 Summary 4 Section 1 Introduction 4 1.1 Background 4 1.2 Research Objectives and Scope 5 1.3 Research Approach 5 1.4 Organization of This Report 6 Section 2 Review of Median Safety Studies 6 2.1 Median Encroachments 9 2.2 Median-Related Crashes 18 2.3 Crash Countermeasures for Improving Median Safety 20 2.4 Road Safety Audits 21 2.5 Median Design Practice 23 Section 3 Survey Results 23 3.1 Survey Method 23 3.2 Response Rate 23 3.3 Survey Summary 37 Section 4 Interdisciplinary Field Reviews 37 4.1 Overview of Interdisciplinary Field Review Approach 37 4.2 Site Selection for Interdisciplinary Field Reviews 38 4.3 Interdisciplinary Field Review Procedure 40 4.4 Site Characteristics for Interdisciplinary Field Review Sites 40 4.5 Interdisciplinary Field Review Results 40 4.6 Interdisciplinary Crash Review Results 55 4.7 Summary of Contributing Factors 56 Section 5 Crash Data Analyses to Investigate Contributing Factors 56 5.1 Crash Analysis Approach 57 5.2 Analysis Results for Median-Related Crashes on Rural Freeways 60 5.3 Comparison of Results for Median-Related Crashes to Other Crash Types 62 5.4 Involvement of Road Surface Condition in Median-Related Crashes and Other Crash Types 62 5.5 Discussion of Contributing Factors 63 Section 6 Guidelines for Geometric Design and Countermeasure Implementation to Reduce Median-Related Crashes 65 Section 7 Conclusions and Recommendations

67 References 70 Abbreviations 71 Appendixes A through C 72 Appendix D Guidelines for Reducing the Frequency and Severity of Median-Related Crashes on Divided Highways Note: Many of the photographs, figures, and tables in this report have been converted from color to grayscale for printing. The electronic version of the report (posted on the Web at www.trb.org) retains the color versions.