Safety Evaluation of Profiled Thermoplastic Pavement Markings

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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 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 implementation of the American Association of State Highway and Transportation Officials (AASHTO) Strategic Highway Safety Plan. The ELCSI-PFS research provides a crash modification factor and benefit–cost economic analysis for each of the targeted safety strategies identified as priorities by the pooled fund member States.

The profiled thermoplastic pavement markings evaluated in this study are intended to reduce the frequency of crashes by improving the visibility of pavement markings and providing a rumble effect. Geometric, traffic, and crash data were obtained from Florida and South Carolina. The combined results for the two States indicate consistent, though statistically insignificant, reductions in nighttime wet-weather crashes, the primary targets of the treatment. The results suggest that the treatment, even with conservative assumptions for cost, service life, and the value of a statistical life, can be cost effective. This document is intended for safety engineers, highway designers, planners, and practitioners at State and local agencies involved with AASHTO Strategic Highway Safety Plan implementation.

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

Technical Report Documentation Page

SI* (Modern Metric) Conversion Factors

Table of Contents

EXECUTIVE SUMMARY

CHAPTER 1. INTRODUCTION

• BACKGROUND ON STRATEGY
• BACKGROUND ON STUDY
• LITERATURE REVIEW

CHAPTER 2. OBJECTIVE

CHAPTER 3. METHODOLOGY

CHAPTER 4. DATA COLLECTION

• FLORIDA
  • Installation Data
  • Reference Sites
  • Roadway Data
  • Traffic Data
  • Crash Data
  • Treatment Cost and Service Life Data
    
    
• SOUTH CAROLINA
  • Installation Data
  • Reference Sites
  • Roadway Data
  • Traffic Data
  • Crash Data
  • Treatment Cost and Service Life Data
  • Data Characteristics and Summary

CHAPTER 5. DEVELOPMENT OF SPFS

• FLORIDA
• SOUTH CAROLINA

CHAPTER 6. BEFORE–AFTER EVALUATION RESULTS

• AGGREGATE ANALYSIS
• DISAGGREGATE ANALYSIS

CHAPTER 7. ECONOMIC ANALYSIS

CHAPTER 8. SUMMARY AND CONCLUSIONS

APPENDIX A. ADDITIONAL INSTALLATION DETAILS FROM FLORIDA

APPENDIX B. ADDITIONAL INSTALLATION DETAILS FROM SOUTH CAROLINA

ACKNOWLEDGEMENTS

REFERENCES

List of Figures

• Figure 1. Photo. Raised profiled thermoplastic marking.⁽¹⁾
• Figure 2. Photo. Inverted profiled thermoplastic marking.⁽¹⁾
• Figure 3. Equation. Estimated change in safety.
• Figure 4. Equation. EB estimate of expected crashes.
• Figure 5. Equation. EB weight.
• Figure 6. Equation. Index of effectiveness.⁽³⁾
• Figure 7. Equation. Standard deviation of index of effectiveness.⁽³⁾
• Figure 8. Equation. Form of SPFs for Florida.
• Figure 9. Equation. Form of SPFs for South Carolina.
• Figure 10. Equation. Aggregate 2015 unit cost for total crashes calculation.

List of Tables

• Table 1. Definitions of crash types by State.
• Table 2. Strategy installation and crash data summary for treatment sites.
• Table 3. Volume and roadway data summary for Florida sites.
• Table 4. Volume and roadway data summary for South Carolina sites.
• Table 5. Data summary for reference sites.
• Table 6. Parameter estimates and SEs for SPFs for Florida two-lane roads.
• Table 7. Parameter estimates and SEs for SPFs for Florida multilane roads.
• Table 8. Parameter estimates and SEs for SPFs for South Carolina two-lane roads.
• Table 9. Parameter estimates and SEs for SPFs for South Carolina multilane roads.
• Table 10. Results for Florida.
• Table 11. Results for South Carolina.
• Table 12. Combined results for Florida and South Carolina.

List of Abbreviations

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 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 (ELCSI-PFS), which functions under the DCMF program.

This study selected profiled thermoplastic pavement markings as a strategy for evaluation. This strategy involved upgrading existing markings from flat-line thermoplastic or other standard markings to the profiled product. These markings are designed to provide an improved level of vision to drivers, particularly during wet-road surface conditions. The profiled nature also provides a rumble effect for errant vehicles. A literature review found no published research evaluating the effect on crashes after profiled thermoplastic pavement markings were applied.

The project team obtained geometric, traffic, and crash data from Florida and South Carolina, where the treatment was applied to edge lines of two-lane and multilane roads. To account for potential selection bias related to regression-to-the-mean, an empirical Bayes (EB) before–after analysis was conducted using reference groups of untreated road sections with characteristics similar 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. The evaluation was done for the following crash types: total, injury, run-off-road (ROR), head-on, sideswipe-opposite-direction, sideswipe-same-direction, wet-road, nighttime wet-road crashes, and all nighttime crashes. None of these crash types included intersection-related, snow/slush/ice, and animal crashes.

Only nighttime wet-road crashes, a principal target crash type, exhibited a material change, with an estimated crash modification factor (CMF) of 0.908. Although the estimated CMF was based on a small sample of crashes and was not statistically significant at the 95-percent confidence level, it was consistent between the two States, which suggests that its use might be justifiable.

The B/C ratio for flat-line thermoplastic markings was 3.65:1, based on the consistent reduction in nighttime wet-road crashes and estimated with conservative cost and service life assumptions. Applying the sensitivity analysis recommended by the U.S. Department of Transportation (USDOT), this value could range from 2.01:1 to 5.04:1. These results suggest that the treatment—even with conservative assumptions on cost, service life, and the value of a statistical life—can be applied cost effectively despite the relatively small crash reduction effects.