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Publication Number:  FHWA-HRT-15-048    Date:  June 2015
Publication Number: FHWA-HRT-15-048
Date: June 2015

 

Safety Evaluation of Centerline Plus Shoulder Rumble Strips

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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). The 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 the implementation of the American Association of State Highway and Transportation Officials Strategic Highway Safety Plan. The ELCSI-PFS studies provide a crash modification factor (CMF) and benefit-cost (B/C) economic analysis for each of the targeted safety strategies identified as priorities by the pooled fund member states.

The combined application of centerline and shoulder rumble strips evaluated under this pooled fund study is intended to reduce the frequency of crashes by alerting drivers that they are about to leave the travelled lane. Geometric, traffic, and crash data were obtained at treated two-lane rural road locations in Kentucky, Missouri, and Pennsylvania. The results of this evaluation show that head-on, run-off-road, and sideswipe-opposite-direction crashes were significantly reduced, and application of centerline and shoulder rumble strips also has potential to reduce crash severity for all types of crashes.

Monique R. Evans, P.E.
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-15-048

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

Safety Evaluation of Centerline Plus Shoulder Rumble Strips

5. Report Date

June 2015

6. Performing Organization Code
7. Author(s)

Lyon, Craig; Bhagwant Persaud; and Kimberly Eccles.

8. Performing Organization Report No.
9. Performing Organization Name and Address

Vanessa Hangen Brustlin, Inc (VHB) Persaud Lyon, Inc
8300 Boone Blvd., Ste. 700 87 Elmcrest Road
Vienna, VA 22182-2626 Toronto, Ontario M9C 3R7

10. Work Unit No.
11. Contract or Grant No.

DTFH61-13-D-00001

12. Sponsoring Agency Name and Address

Office of Safety Research and Development Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

13. Type of Report and Period

Safety Evaluation

14. Sponsoring Agency Code:

FHWA

15. Supplementary Notes.

The Federal Highway Administration (Office of Safety Research and Development) managed this study. The project team members were Craig Lyon, Dr. Bhagwant Persaud, Kimberly Eccles, and Jonathan Soika. The FHWA Office of Safety Research and Development Contract Task Order Manager was Roya Amjadi.

16. Abstract

The Federal Highway Administration organized a pooled fund study of 38 States to evaluate low-cost safety strategies as part of its strategic highway safety effort. One of the strategies selected for evaluation was the combined application of centerline and shoulder rumble strips. This strategy is intended to reduce the frequency of crashes by alerting drivers that they are about to leave the travelled lane. Geometric, traffic, and crash data were obtained at treated two-lane rural road locations in Kentucky, Missouri, and Pennsylvania. To account for potential selection bias and regression-to-the-mean, an Empirical Bayes before-after analysis was conducted, using reference groups of untreated two-lane rural roads with similar characteristics to the treated sites. The analysis also controls for changes in traffic volumes over time and time trends in crash counts unrelated to the treatment. The combined results for all States indicate statistically significant crash reductions for all crash types analyzed. The crash type with the smallest crash modification factor (CMF) (i.e., the greatest crash reduction) is head-on, with a CMF of 0.632. Run-off-road and sideswipe-opposite-direction crashes have estimated CMFs of 0.742 and 0.767, respectively. For run-off-road, head-on, and sideswipe-opposite-direction crashes combined (i.e., lane departure crashes), the estimated CMF is 0.733. For all crash types combined, CMFs of 0.800 for all severities and 0.771 for fatal+injury were estimated. Intersection-related and animal crashes were excluded from the evaluation. Benefit-cost ratios were estimated to range from 20.2 to 54.7, depending on the treatment cost and service life assumption, which varied by State. These results are based on conservative service life assumptions.

17. Key Words:

Rumble strips, low-cost, safety improvements, safety evaluations, Empirical Bayesian.

18. Distribution Statement

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

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No. of Pages:

59

22. Price
Form DOT F 1700.7 Reproduction of completed page authorized

 

SI* (Modern Metric) Conversion Factors

 

Table of Contents

List of figures

LIST OF TABLES

LIST OF ABBREVIATIONS

AADTAverage annual daily traffic  
B/CBenefit-cost  
C-GComparison group  
CLRSCenterline rumble strips  
CMFCrash modification factor  
EBEmpirical Bayes  
FIFatal+injury  
FHWAFederal Highway Administration  
GISGeographic information system  
KYTCKentucky Transportation Cabinet  
MoDOTMissouri Department of Transportation  
NCHRPNational Cooperative Highway Research Program  
PDOProperty Damage Only  
PennDOTPennsylvania Department of Transportation  
SPFSafety performance functions  
SRSShoulder rumble strip  
SVRORSingle-vehicle run-off-road  

List of Symbols

Δ Greek letter delta
λ Greek letter lambda
π Greek letter pi
θ Greek letter theta

Executive Summary

The Federal Highway Administration (FHWA) organized a pooled fund study of 38 States to evaluate low-cost safety strategies as part of its strategic highway safety effort. The purpose of the FHWA Low-Cost Safety Improvements Pooled Fund Study is to evaluate the safety effectiveness of several low-cost safety strategies through scientifically rigorous crash-based studies. One of the strategies selected for evaluation for this study was the application of shoulder rumble strips (SRS) and centerline rumble strips (CLRS) in combination. This strategy is intended to reduce the frequency of crashes by alerting drivers that they are about to leave the travelled lane. While research has been published on the safety effectiveness of SRS or CLRS used in isolation, the effectiveness of the combined treatment has not been shown.

Geometric, traffic, and crash data were obtained at treated two-lane rural road locations in Kentucky, Missouri and Pennsylvania. To account for potential selection bias and regression-to-the-mean, an Empirical Bayes (EB) before-after analysis was conducted using reference groups of untreated two-lane rural roads with similar characteristics to the treated sites. A slightly different approach was required for the analysis of the treatment sites in Missouri, which is installing rumble strips on two-lane rural roads whenever a resurfacing project is undertaken. As a result, a suitable reference group with no rumble strips for this road type presently or in the near future did not exist. The analysis also controls for changes in traffic volumes over time and time trends in crash counts unrelated to the treatment.

The combined results for all States indicate reductions in crashes for all crash types analyzed that are statistically significant at the 95-percent confidence level (i.e., 5-percent significance level). The crash type with the smallest crash modification factor (CMF) (i.e., the great crash reduction) is head-on, with a CMF of 0.632. Run-off-road and sideswipe-opposite-direction crashes have estimated CMFs of 0.742 and 0.767, respectively. For run-off-road, head-on, and sideswipe-opposite-direction crashes combined (i.e., lane departure crashes), the estimated CMF is 0.733. For all crash types combined, CMFs of 0.800 for all severities and 0.771 for fatal+injury (FI) were estimated. It is important to remember that all crash types considered exclude intersection-related and animal crashes.

The disaggregate analysis sought to identify those conditions under which the treatment is most effective. Run-off-road, head-on, and sideswipe-opposite-direction crashes were the focus of this analysis because they are the focus of this treatment. The analysis found no clear trend between the CMF and values for posted speed, lane width, or shoulder width. Larger percentage crash reductions were found for run-off-road crashes at higher average annual daily traffic (AADT). For head-on+sideswipe-opposite-direction crashes, the trend is reversed with smaller percentage crash reductions at higher AADTs.

For the expected crash frequency, larger percentage crash reductions were found for run-off-road crashes for higher crash frequencies. For head-on+sideswipe-opposite-direction crashes, the trend is reversed with smaller percentage crash reductions at higher crash rates. Because expected crashes increase with volume as seen in the Safety Performance Functions (SPF) developed, the trend of lower percentage crash reductions at higher crash rates for head-on+sideswipe-opposite-direction crashes would be expected given the results for AADT.

Benefit-cost (B/C) ratios are estimated to range from 20.2 for a higher cost/higher service life assumption (based on Kentucky information) to 54.7 for a lower cost/lower service life assumption (based on information from Missouri). These results, which are based on conservative service life assumptions, suggest that the treatment, even in its most expensive variations, can be highly cost effective.

 

 

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