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Publication Number:  FHWA-HRT-17-069    Date:  December 2017
Publication Number: FHWA-HRT-17-069
Date: December 2017

 

Safety Evaluation of Edge-Line Rumble Stripes on Rural Two-Lane Horizontal Curves

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FOREWORD

The research documented in this report was conducted as part of the Federal Highway Administration’s (FHWA) Evaluation of Low-Cost Safety Improvements Pooled Fund Study (ELCSI-PFS). FHWA established this PFS 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 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 edge-line rumble stripes (ELRSs) on rural two-lane horizontal curves. ELRSs are a variation of common shoulder rumble strips used to alert drowsy or distracted drivers when they are leaving the travel lane to the right. ELRSs are installed with the edge-line pavement marking placed directly over the rumble strip. Data were obtained at treated rural two-lane horizontal curves in Kentucky and Ohio. The results for Kentucky indicate statistically significant reductions for total, injury, run-off-road (ROR), and nighttime crashes. The results for Ohio indicate statistically significant reductions for all crash types (i.e., total, injury, ROR, nighttime, and nighttime ROR). The B/C analysis results suggest that this treatment can be highly cost-effective. This report is intended for State departments of transportation, transportation agencies, academics, researchers, and other practitioners.

Jonathan Porter, Ph.D.
Acting Director, Office of Safety
Research and Development

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation (USDOT) 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-17-069

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

Safety Evaluation of Edge-Line Rumble Stripes on Rural Two-Lane Horizontal Curves

5. Report Date

December 2017

6. Performing Organization Code
7. Author(s)

Scott Himes, Frank Gross, 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

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; 2014–2016

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 Contracting Officer’s Program and Task Manager was Roya Amjadi (HRDS-20).

16. Abstract

The Development of Crash Modification Factors (DCMF) program conducted safety evaluations of edge-line rumble stripes (ELRSs) on rural two-lane horizontal curves for the Evaluation of Low-Cost Safety Improvements Pooled Fund Study. This study evaluated the application of ELRSs on rural two-lane horizontal curves. ELRSs are a variation of common shoulder rumble strips used to alert drowsy or distracted drivers when they are leaving the travel lane to the right. ELRSs are installed with the edge-line pavement marking placed directly over the rumble strip. Geometric, traffic, and crash data were obtained at treated rural two-lane horizontal curves in Kentucky and Ohio. To account for potential selection bias and regression-to-the-mean, an empirical Bayes before–after analysis was conducted using reference groups of untreated rural horizontal curves with similar characteristics to the treated sites. The analysis also controlled for changes in traffic volumes over time and time trends in crash counts unrelated to the treatment. Owing to a small sample for the reference group in Kentucky and a simultaneous statewide curve warning sign upgrade program in Ohio, alternative reference sites were used to account for annual trends. The results for Kentucky indicated statistically significant reductions for total, injury, run-off-road (ROR), and nighttime crashes, with crash modification factors (CMFs) of 0.75, 0.64, 0.74, and 0.63, respectively. The results for Ohio indicated statistically significant reductions for all crash types, with total, injury, ROR, nighttime, and nighttime ROR CMFs of 0.79, 0.79, 0.78, 0.75, and 0.71, respectively. The two States’ results could not be combined because of the statewide curve signing program in Ohio. It is important to note that all crash types considered in this research excluded intersection-related and animal crashes. Benefit–cost (B/C) ratios were estimated to be 331:1 for Kentucky and 477:1 for Ohio. If ELRSs were used as a curve-specific treatment, the B/C ratio would likely be much smaller because of the higher installation cost; however, these results suggest that the treatment can be highly cost effective.

17. Key Words

ELRS, two-lane rural roads, horizontal curves, distracted driver, rumble strips, rumble stripes, low-cost, safety improvements, empirical Bayesian.

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

61

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 Safety Performance Functions

Chapter 7. Before–After Evaluation Results

Chapter 8. Economic Analysis

Chapter 9. Summary and Conclusions

Appendix: Additional Installation Details

Acknowledgements

References

LIST OF FIGURES

LIST OF TABLES

LIST OF ABBREVIATIONS

AADT

average annual daily traffic

AASHTO

American Association of State Highway and Transportation Officials

B/C

benefit–cost

C-G

comparison group

CLRS

center-line rumble strip

CMF

crash modification factor

DCMF

Development of Crash Modification Factors (program)

EB

empirical Bayes

ELCSI-PFS

Evaluation of Low-Cost Safety Improvements Pooled Fund Study

ELRS

edge-line rumble stripe

FHWA

Federal Highway Administration

FTM

flat thermoplastic edge marking

GIS

geographic information system

HPMS

Highway Performance Monitoring System

HSIS

Highway Safety Information System

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, O is property damage only)

KYTC

Kentucky Transportation Cabinet

MUTCD

Manual on Uniform Traffic Control Devices

NCHRP

National Cooperative Highway Research Program

ODOT

Ohio Department of Transportation

PFS

pooled fund study

ROR

run-off-road

SE

standard error

SPF

safety performance function

SRS

shoulder rumble strip

SVROR

single-vehicle run-off-road

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 new strategies for statewide safety improvements. Forty State transportation departments have provided technical feedback on safety improvements to the DCMF program and have implemented 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 edge-line rumble stripes (ELRSs) on rural two-lane horizontal curves. ELRSs are a variation of common shoulder rumble strips (SRSs) used to alert drowsy or distracted drivers when they leave the travel lane to the right. ELRSs are installed where edge-line pavement markings would normally be placed, and the pavement marking is installed directly over the rumble strip. In this way, the ELRSs are installed closer to the travel lane than common SRSs. In addition, the vertical faces that are created within the milled rumble strip to which pavement markings are applied have the effect of enhancing the visibility of the edge line during nighttime and wet-weather conditions.

The project team obtained geometric, traffic, and crash data at treated rural horizontal curve locations in Kentucky and Ohio. To account for potential selection bias and regression-to-the-mean, the project team conducted an empirical Bayes (EB) before–after analysis using reference groups of untreated rural horizontal curves with similar characteristics to the treated sites. The analysis also controlled for changes in traffic volumes over time and time trends in crash counts unrelated to the treatment. While the analysis focused on the safety effectiveness on horizontal curves, the treatment applications were not limited only to horizontal curves. The treatment was a corridor treatment applied to segments consisting of both tangents and curves; however, the analysis removed horizontal tangents and only considered the effectiveness on curves.

The results for Kentucky indicated statistically significant reductions for total, injury, run-off-road (ROR), and nighttime crashes at the 95-percent confidence level. Nighttime crashes had the smallest crash modification factor (CMF), or the greatest reduction, with a value of 0.63. Total, injury, and ROR crashes had CMFs of 0.75, 0.64, and 0.74, respectively. The CMF for nighttime ROR crashes was 0.75 and was consistent with the same CMF from Ohio; however, it was significant only at the 80-percent level, suggesting that sample size was the reason for the lack of statistical significance at the 95-percent level. The results for Ohio indicated statistically significant reductions for all crash types. Nighttime ROR crashes had the smallest CMF of 0.71. Total, injury, ROR, and nighttime crashes had CMFs of 0.79, 0.79, 0.78, and 0.75, respectively. The resulting Ohio installation CMFs reflected the installation of ELRSs on horizontal curves as well as the impact of the statewide signing program. It is also important to note that all crash types considered in this research excluded intersection-related and animal crashes.

A disaggregate analysis of the results indicated larger safety benefits for horizontal curves with average annual daily traffic (AADT) greater than 4,000 for all crash types; however, the differences by AADT were not statistically significant at the 95-percent confidence level. The disaggregate analysis further indicated larger safety benefits for horizontal curves with a higher before-period expected crash frequency. The results suggested no benefit for curves with low before-period expected crash frequencies for all crash types. The difference in CMFs between low before-period expected crash frequency and high before-period expected crash frequency was statistically significant for total and ROR crashes. Due to correlation between variables, caution should be used in interpreting and applying these disaggregate results; however, the disaggregate analysis CMFs may be used to inform the process of prioritizing treatment sites for ELRSs.

Estimated B/C ratios range from 189:1 to 467:1 for Kentucky and from 272:1 to 672:1 for Ohio. On first inspection, the B/C ratios were larger than expected for an installation of this type. However, the installations took place on corridors, while the analysis only looked at the safety effects on horizontal curves. Horizontal curves have higher crash rates than overall corridors, and the cost per mile of installation would not be representative for installations only on horizontal curves. As a curve-specific treatment, the B/C ratio would likely be reduced owing to the higher deployment cost for spot-specific installations. Regardless, these results suggest that the treatment, even in its most expensive variation, can be highly cost effective.

 

 

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