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Publication Number:  FHWA-HRT-17-070    Date:  August 2017
Publication Number: FHWA-HRT-17-070
Date: August 2017

 

Safety Evaluation of Cable Median Barriers in Combination With Rumble Strips on Divided Roads

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FOREWORD

The research documented in this report was conducted as part of the Federal Highway Administration (FHWA) Evaluation of Low-Cost Safety Improvements Pooled Fund Study (ELCSI-PFS). FHWA established this pooled fund study in 2005 to conduct research on the effectiveness of the safety improvements identified by the National Cooperative Highway Research Program Report 500 guides as part of implementation of the American Association of State Highway and Transportation Officials Strategic Highway Safety Plan. The ELCSI-PFS research provides a crash modification factor and benefit-cost (B/C) economic analysis for each of the targeted safety strategies identified as priorities by the pooled fund member States.

This study evaluated application of cable median barriers in combination with rumble strips on the inside shoulder of divided roads. This strategy is intended to reduce the frequency of cross-median crashes, which tend to be very severe. Data were obtained in Illinois, Kentucky, and Missouri. In Illinois and Kentucky, cable median barriers were introduced many years after the inside shoulder rumble strips were installed; therefore, the evaluation determined the safety effect of implementing cable barriers along sections that already had rumble strips. Conversely, in Missouri, the inside shoulder rumble strips and cable barrier were implemented around the same time. The evaluation in Missouri determined the combined safety effect of both strategies. The combined Illinois and Kentucky results indicate an increase in total crashes but a decrease in injury and fatal crashes and head-on plus opposite-direction sideswipe crashes (used as a proxy for cross-median crashes). The results from Missouri for total and injury and fatal crashes were very similar to the combined Illinois and Kentucky results. However, the reduction in cross-median crashes in Missouri was much more dramatic. The economic analysis for B/C ratios shows that this strategy is cost beneficial.

Monique R. Evans
Director, Office of Safety
Research and Development

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.

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 Report Documentation Page

1. Report No.

FHWA-HRT-17-070

2. Government Accession No. 3 Recipient's Catalog No.
4. Title and Subtitle

Safety Evaluation of Cable Median Barriers in Combination with Rumble Strips on Divided Roads

5. Report Date

August 2017

6. Performing Organization Code
7. Author(s)

Raghavan Srinivasan, Bo Lan, Daniel Carter, Bhagwant Persaud, and Kimberly Eccles

8. Performing Organization Report No.

 

9. Performing Organization Name and Address

VHB
8300 Boone Boulevard, Suite 700
Vienna, VA 22182-2626
  Persaud & Lyon, Inc
87 Elmcrest Road
Toronto, ON M9C 3R7

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

DTFH61-13-D-00001

12. Sponsoring Agency Name and Address

U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590-3660

13. Type of Report and Period Covered

Safety Evaluation

14. Sponsoring Agency Code

 

15. Supplementary Notes

The Federal Highway Administration (FHWA) Office of Safety Research and Development managed this study under the Development of Crash Modification Factors program. The FHWA Office of Safety Research and Development Program and Task Manager was Roya Amjadi.

16. Abstract

The Development of Crash Modification Factors program conducted the safety evaluation of cable median barriers in combination with rumble strips on the inside shoulder of divided roads for the Evaluation of Low Cost Safety Improvements Pooled Fund Study. This study evaluated safety effectiveness of cable median barriers in combination with rumble strips on the inside shoulders of divided roads. This strategy is intended to reduce the frequency of cross-median crashes, which tend to be very severe. Geometric, traffic, and crash data were obtained for divided roads in Illinois, Kentucky, and Missouri. To account for potential selection bias and regression-to-the-mean, an empirical Bayes before–after analysis was conducted using reference groups of untreated roads with characteristics similar to those of the treated sites. The analysis also controlled for changes in traffic volumes over time and time trends in crash counts unrelated to the treatment. In Illinois and Kentucky, cable median barriers were introduced many years after the inside shoulder rumble strips were installed; therefore, the evaluation determined the safety effect of implementing cable barriers along sections that already had rumble strips. Conversely, in Missouri, the inside shoulder rumble strips and cable barrier were implemented around the same time. Hence, the evaluation in Missouri determined the combined safety effect of inside shoulder rumble strips and cable barriers. The combined Illinois and Kentucky results indicate about a 27-percent increase in total crashes; a 24-percent decrease in fatal, incapacitating, non-incapacitating, and possible injury crashes; a 22-percent decrease in fatal, incapacitating, and non-incapacitating injury crashes; and a 48-percent decrease in head-on plus opposite-direction sideswipe crashes (used as a proxy for cross-median crashes). The results from Missouri for total and injury and fatal crashes were very similar to the combined Illinois and Kentucky results. However, the reduction in cross-median crashes in Missouri was much more dramatic, showing a 96-percent reduction (based on cross-median indicator only) and an 88-percent reduction (based on cross-median indicator plus head-on). The economic analysis for benefit-cost ratios shows that this strategy is cost beneficial.

17. Key Words

Rumble strips, cross-median crashes, low-cost, safety improvements, safety evaluations, empirical Bayesian, cross-median, head-on, sideswipe, injury, cable barrier, median barrier

18. Distribution Statement

No restrictions. This document is available through the National Technical Information Service,
Springfield, VA 22161.
http://www.ntis.gov

19. Security Classification
(of this report)

Unclassified

20. Security Classification
(of this page)

Unclassified

21. No. of Pages

71

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

SI* (Modern Metric) Conversion Factors

Table of Contents

EXECUTIVE SUMMARY

CHAPTER 1. INTRODUCTION

CHAPTER 2. OBJECTIVE

CHAPTER 3. STUDY DESIGN

CHAPTER 4. METHODOLOGY

CHAPTER 5. DATA COLLECTION

CHAPTER 6. DEVELOPMENT OF SPFS

CHAPTER 7. BEFORE–AFTER EVALUATION RESULTS

CHAPTER 8. ECONOMIC ANALYSIS

CHAPTER 9. SUMMARY AND CONCLUSIONS

APPENDIX A. ADDITIONAL INSTALLATION DETAILS FROM ILLINOIS

APPENDIX B. ADDITIONAL INSTALLATION DETAILS FROM KENTUCKY

APPENDIX C. ADDITIONAL INSTALLATION DETAILS FROM MISSOURI

APPENDIX D. METHODOLOGY FOR CALCULATING CRASH COSTS

ACKNOWLEDGMENTS

REFERENCES

List of Figures

List of Tables

List of Abbreviations

AADT

annual average daily traffic

B/C

benefit-cost

CMF

crash modification factor

EB

empirical Bayes

ELCSI-PFS

Evaluation of Low-Cost Safety Improvements Pooled Fund Study

FARS

Fatality Analysis Reporting System

FHWA

Federal Highway Administration

GIS

geographic information system

HSIS

Highway Safety Information System

IDOT

Illinois Department of Transportation

KABCO

Scale used to represent injury severity in crash reporting (K is fatal injury, A is incapacitating injury, B is non-incapacitating injury, C is possible injury, and O is property damage only)

KYTC

Kentucky Transportation Cabinet

MoDOT

Missouri Department of Transportation

NCHRP

National Cooperative Highway Research Program

PDO

property damage only

ROR

run-off-road

SE

standard error

SPF

safety performance function

SVROR

single-vehicle run-off-road

USDOT

U.S. Department of Transportation

VSL

value of a statistical life

Executive Summary

The Federal Highway Administration (FHWA) established the Development of Crash Modification Factors (DCMF) program in 2012 to address highway safety research needs for evaluating new and innovative safety strategies (improvements) by developing reliable quantitative estimates of their effectiveness in reducing crashes. The ultimate goal of the DCMF program is to save lives by identifying new safety strategies that effectively reduce crashes and promote those strategies for nationwide implementation by providing measures of their safety effectiveness and benefit-cost (B/C) ratios through research. State transportation departments and other transportation agencies need to have objective measures for safety effectiveness and B/C ratios before investing in broad applications of new strategies for safety improvements. Forty State transportation departments provide technical feedback on safety improvements to the DCMF program and implement new safety improvements to facilitate evaluations. These States are members of the Evaluation of Low-Cost Safety Improvements Pooled Fund Study, which functions under the DCMF program. This study evaluated the application of cable median barriers in combination with rumble strips on the inside shoulders of divided roads. This strategy is intended to reduce the frequency of crashes by reducing the frequency and severity of cross-median crashes.

The research team obtained geometric, traffic, and crash data at treated multilane divided roads in Illinois, Kentucky, and Missouri. To account for potential selection bias and regression- to-the-mean, the research team conducted an empirical Bayes (EB) before–after analysis using reference groups of untreated multilane lane roads with characteristics similar to those of the treated sites. The analysis of the treatment sites in Missouri required a slightly different approach because Missouri installed cable median barriers and inside shoulder rumble strips on a systemwide basis on certain types of roads. As a result, there was no suitable reference group without the treatment for this road type. The analysis also controlled for changes in traffic volumes over time and time trends in crash counts unrelated to the treatment.

Illinois and Kentucky introduced cable median barriers many years after the inside shoulder rumble strips were installed; therefore, the evaluation determined the safety effect of implementing cable barrier along sections that already had rumble strips. Missouri implemented the inside shoulder rumble strips and cable barriers around the same time; as a result, the Missouri evaluation determined the combined safety effect of inside shoulder rumble strips and cable barriers. The combined Illinois and Kentucky results indicate about a 27-percent increase in total crashes, a 22- to 24-percent decrease in injury and fatal crashes (depending on whether injury crashes were defined as KAB or KABC), and a 48-percent decrease in cross-median crashes (defined as head-on plus opposite-direction sideswipe crashes).[1] The results from Missouri for total and injury and fatal crashes were very similar to the combined Illinois and Kentucky results. However, the reduction in cross-median crashes in Missouri was more dramatic, with a 96-percent reduction (based on cross-median indicator only) and an 88-percent reduction (based on cross-median indicator plus head-on). The research team estimates the B/C ratios to be about 8.28 for the treatment in Illinois and Kentucky and 4.14 for the treatment in Missouri.


[1] The KABCO Scale is used to represent injury severity in crash reporting (K is fatal injury, A is incapacitating injury, B is non-incapacitating injury, C is possible injury, and O is property damage only).

 

 

 

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