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Publication Number: FHWA-HRT-11-024
Date: April 2011

Safety Evaluation of the Safety Edge Treatment

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FOREWORD

Advancing the safety of America’s highways is a top priority for the Federal Highway Administration (FHWA). Through roadway design, cost-effective countermeasures, and advanced analytical practices, the FHWA Office of Safety Research and Development supports this objective by encouraging the development and implementation of improvements, such as the safety edge, that exhibit real safety benefits for the driving public.

This study evaluated the safety effectiveness of the safety edge treatment in conjunction with resurfacing, a cost-effective safety improvement that can reduce crashes and fatalities. Development of the safety edge treatment was based on a need to reduce drop-off-related crashes and on engineering judgment. The evaluation utilized a before-after empirical Bayes analysis for determining a crash reduction factor for this roadway treatment. Furthermore, the study conducted a benefit-cost analysis to determine the advantages of applying this treatment to rural highways. This analysis of the safety edge highlights the benefits of a low-cost improvement through improved roadway design and evaluation.

This report will interest safety and highway agency engineers who have a shared responsibility for public safety and an interest in implementing low-cost roadway safety treatments.

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. This report does not constitute a standard, specification, or regulation.

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-11-024

2. Government Accession No.

3. Recipient's Catalog No.

4. Title and Subtitle

Safety Evaluation of the Safety Edge Treatment

5. Report Date

March 2011

6. Performing Organization Code:

440545878

7. Author(s)

J.L. Graham, K.R. Richard, M.K. O'Laughlin, and D.W. Harwood

8. Performing Organization Report No.

110495.1.001

9. Performing Organization Name and Address

MRIGlobal

425 Volker Blvd.

Kansas City, MO 64110

10. Work Unit No.

11. Contract or Grant No.

DTFH61-06-C-00013

12. Sponsoring Agency Name and Address

Federal Highway Administration

Turner-Fairbank Highway Research Center

Office of Safety Research and Development

6300 Georgetown Pike

McLean, VA 22101-2296

13. Type of Report and Period Covered

Final Report, 9/1/2006-7/31/2010

14. Sponsoring Agency Code

HRDS-20

15. Supplementary Notes

The FHWA Contracting Officer's Technical Representative (COTR) was Carol Tan, HRDS-20.

16. Abstract

Between periods of maintenance, pavement-edge drop-offs can form along the edge of highways. When a driver runs off the roadway, such drop-offs can hinder reentry and may lead to driver overcorrection, loss of control, or overturning on the roadway or roadside. The safety edge is a treatment that is implemented in conjunction with pavement resurfacing and is intended to help minimize drop-off-related crashes.

This report examines the safety effects, costs, and benefits of this low-cost treatment for two-lane and multilane rural highways. The safety research was conducted as an observational before-after evaluation of treated sites using the empirical Bayes method. The economic appraisal consisted of a benefit-cost analysis.

The safety evaluation found that the safety edge treatment appears to have a small positive crash reduction effect. The best effectiveness measure for the safety edge treatment was a 5.7 percent reduction in total crashes on rural two-lane highways. However, this result was not statistically significant. The economic analysis showed that the treatment is very inexpensive and that its application is highly cost-effective for a broad range of conditions on two-lane highways. Inconsistent results were found for rural multilane highways due to a small data sample.

17. Key Words

Safety edge, Pavement-shoulder drop-off, Pavement resurfacing, Run-off-road crash

18. Distribution Statement

No restrictions. This document is available through the National Technical Information Service, Springfield, VA 22161.

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No. of Pages

95

22. Price

N/A

Form DOT F 1700.7 (8-72)

Reproduction of completed page authorized

SI* (Modern Metric) Conversion Factors

Table of Contents

Chapter 1. Background and Research Objectives

Chapter 2. Project Database

Chapter 3. Preliminary Analysis Results for Field Measurements of Pavement-Edge Drop-Offs

Chapter 4. Analysis Results for Safety Evaluation

Chapter 5. Estimated Cost of the Safety Edge Treatment

Chapter 6. Benefit-Cost Analysis

Chapter 7. Conclusions

Chapter 8. Recommendations

Appendix A. Identification of Drop-Off-Related Crashes

Appendix B. Pavement-Edge Drop-Off Data Collection Methodology

Appendix C. Scatter Plots of Accidents and AADT

References

List of figures

Figure 1. Diagram. Safety edge detail

Figure 2. Graph. Drop-off height measurement distributions for two-lane highways with paved shoulders in Georgia

Figure 3. Graph. Comparison of Georgia SPFs by crash severity and roadway and shoulder type

Figure 4. Graph. Comparison of Indiana SPFs by crash severity and roadway and shoulder type

Figure 5. Diagram. Typical cross section for the safety edge treatment on one side of the road

Figure 6. Graph. Minimum benefit-cost ratios for the safety edge treatment as a function of AADT

Figure 7. Graph. Maximum benefit-cost ratios for the safety edge treatment as a function of AADT

Figure 8. Illustration. Sample data collection form

Figure 9. Illustration. Data collection intervals

Figure 10. Illustration. Measurement of drop-off perpendicular to pavement surface

Figure 11. Photo. Measurement of pavement-edge drop-off height

Figure 12. Graph. Georgia multilane roadway with paved shoulder

Figure 13. Graph. Georgia two-lane roadway with paved shoulder

Figure 14. Graph. Georgia two-lane roadway with unpaved shoulder

Figure 15. Graph. Indiana two-lane roadway with paved shoulder

Figure 16. Graph. Indiana two-lane roadway with unpaved shoulder

List of tables

Table 1. Summary of number and total length of sites

Table 2. Summary of total non-intersection crash data for study sites

Table 3. Summary of fatal and injury non-intersection crash data for study sites

Table 4. Summary of traffic volume data for study sites

Table 5. Summary of lane widths for study sites

Table 6. Comparison of the proportions of drop-off heights exceeding 2 inches for the period before resurfacing.

Table 7. Summary of pavement-edge drop-off height measurements

Table 8. Comparison of the proportions of drop-off heights exceeding 2 inches between the before and after resurfacing periods

Table 9. Comparison of the proportions of drop-off heights exceeding 2 inches between treatment and comparison sites for the final period after resurfacing

Table 10. SPFs for Georgia sites

Table 11. SPFs for Indiana sites

Table 12. Run-off-road and drop-off-related crash frequencies as a proportion of total crashes

Table 13. Georgia SPF calibration factors

Table 14. Indiana SPF calibration factors

Table 15. Evaluation of treatment versus comparison site effect for the period before resurfacing using EB-adjusted crash frequencies

Table 16. Evaluation of treatment versus comparison site effect for the period before resurfacing using observed crash frequencies

Table 17. Before-after EB evaluation results for total crashes

Table 18. Before-after EB evaluation results for fatal and injury crashes

Table 19. Before-after EB evaluation results for PDO crashes

Table 20. Before-after EB evaluation results for total run-off-road crashes

Table 21. Before-after EB evaluation results for fatal and injury run-off-road crashes

Table 22. Before-after EB evaluation results for PDO run-off-road crashes

Table 23. Before-after EB evaluation results for total drop-off-related crashes

Table 24. Before-after EB evaluation results for fatal and injury drop-off-related crashes

Table 25. Before-after EB evaluation results for PDO drop-off-related crashes

Table 26. Summary of safety effects from year 3, year 2, and year 1 results for before-after EB safety evaluations

Table 27. Cross-sectional analysis of safety edge treatment effect for the period after resurfacing

Table 28. Comparison of proportions of fatal and injury crashes before and after resurfacing

Table 29. Summary of Georgia resurfacing project costs (2005)

Table 30. Summary of Indiana resurfacing project costs (2005)

Table 31. Summary of New York resurfacing project costs (2005)

Table 32. Summary of combined Georgia, Indiana, and New York resurfacing project costs (2005)

Table 33. SPFs used in benefit-cost analysis

Table 34. Benefit-cost analysis for application of safety edge treatment on Georgia two-lane roadways with paved shoulders

Table 35. Benefit-cost analysis for application of safety edge treatment on Indiana two-lane roadways with paved shoulders

Table 36. Benefit-cost analysis for application of safety edge treatment on Georgia two-lane roadways with unpaved shoulders

Table 37. Benefit-cost analysis for application of safety edge treatment on Indiana two-lane roadways with unpaved shoulders

Table 38. Classification criteria for crashes

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