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Publication Number:  FHWA-HRT-17-077    Date:  November 2017
Publication Number: FHWA-HRT-17-077
Date: November 2017

 

Safety Evaluation of Red-Light Indicator Lights (RLILs) At Intersections

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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 red-light indicator lights (RLILs). RLILs are auxiliary lights mounted on signal heads, mast arms, or poles that were connected to a traffic-control signal. This strategy is to reduce the frequency of crashes resulting from drivers disobeying traffic signals by providing a safer means for police to enforce the red interval. The RLIL activates at the onset of the red phase and allows an enforcement officer to observe red-light running from downstream of the intersection. Results indicate statistically significant crash reductions for most crash types (i.e., total crashes, fatal and injury crashes, right-angle, and left-turn). The B/C ratio estimated with conservative cost and service life assumptions indicates this strategy was highly beneficial for four-legged signalized intersections. This report will benefit traffic engineers, enforcement personnel, and safety planners by providing insight for greater intersection safety.

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-17-077

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

Safety Evaluation of Red-Light Indicator Lights (RLILs) at Intersections

5. Report Date

November 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

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 red-light indicator lights (RLILs) at intersections for the Evaluation of Low-Cost Safety Improvements Pooled Fund Study. This study evaluated safety effectiveness of RLILs. RLILs are auxiliary lights mounted on signal heads, mast arms, or poles that are directly connected to a traffic-control signal. The RLIL activates at the onset of the red phase and allows an enforcement officer to observe red-light running from downstream of the intersection. This strategy is intended to reduce the frequency of crashes resulting from drivers disobeying traffic signals by providing a safer and more efficient means for police to enforce the red interval. Geometric, traffic, and crash data were obtained at treated four-legged signalized intersections in Florida. To account for potential selection bias and regression-to-the-mean, an empirical Bayes before–after analysis was conducted using reference groups of untreated four-legged signalized intersections 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. Results indicate statistically significant crash reductions for most crash types. Disobeyed signal crashes had an estimated crash modification factor (CMF) of 0.71. Total crashes, fatal and injury crashes, right-angle, and left-turn crashes had estimated CMFs of 0.94, 0.86, 0.91, and 0.60, respectively. The benefit-cost ratio estimated with conservative cost and service life assumptions was 92:1 for four-legged signalized intersections. The results suggest that the treatment, even with conservative assumptions on cost, service life, and the value of a statistical life, can be cost effective. In addition to the crash-related benefits, RLILs can improve the efficiency and safety of red-light running enforcement efforts. While this study did not evaluate the efficiency and safety impacts with respect to enforcement, it should be noted that RLILs do allow police to observe violators from a downstream position, eliminating the need for a second observer (upstream) and the need to pursue a violator through the red light.

17. Key Words

Intersection, running red-light, red-light indicators, signal indicator lights, enforcement lights, low-cost, safety improvements, safety evaluations, 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

53

22. Price
Form DOT F 1700.7 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. Additional Installation Details

Acknowledgments

References

LIST OF FIGURES

LIST OF TABLES

LIST OF ABBREVIATIONS

AADT

average annual daily traffic

B/C

benefit–cost

CAR

Crash Analysis Reporting (system)

CMF

crash modification factor

DOT

Department of Transportation

EB

empirical Bayes

FDOT

Florida Department of Transportation

FHWA

Federal Highway Administration

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)

LED

light-emitting diode

RLILs

red-light indicator lights

SE

standard error

SPF

safety performance function

USDOT

U.S. Department of Transportation

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

This study investigated the safety effectiveness of red-light indicator lights (RLILs). RLILs are auxiliary lights mounted on signal heads, mast arms, or poles that are directly connected to a traffic-control signal. The RLIL activates at the onset of the red phase and allows an enforcement officer to observe red-light running from downstream of the intersection. This strategy is intended to reduce the frequency of crashes resulting from drivers disobeying traffic signals by providing a safer and more efficient means for police to enforce the red interval. Moreover, for the strategy to be effective, agencies should educate drivers of their existence and intent. Few studies have explored the safety effectiveness of RLILs; in particular, no studies have shown the crash-based safety effectiveness for four-legged intersections.

The research team obtained geometric, traffic, and crash data at treated four-legged rural and urban intersections in Florida. To account for potential selection bias and regression-to-the-mean (RTM), the research team conducted an empirical Bayes (EB) before–after analysis using reference groups of untreated four-legged signalized intersections 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.

The results indicate reductions for all crash types analyzed except rear-end crashes. Reductions were statistically significant at the 95-percent confidence level for all crash types. The crash type with the smallest crash modification factor (CMF)—which translated to the greatest reduction—was left-turn crashes with a CMF of 0.60. For all crash types combined, the research team estimated a CMF of 0.94. The CMFs for disobeyed signal, fatal and injury, right-angle, and nighttime crashes were 0.71, 0.86, 0.91, and 0.89, respectively. The research team estimated an insignificant CMF of 1.016 for rear-end crashes.

A disaggregate analysis sought to identify those conditions under which the treatment was most effective. Because total, fatal and injury, right-angle, and disobeyed signal crashes were the focus of this treatment, these crash types were the focus of the disaggregate analysis. The disaggregate analysis showed that CMFs decreased over the first few years of treatment, indicating that they were more effective in reducing crashes as drivers became accustomed to them. The smallest CMFs (i.e., the greatest reductions) found were for the only district with agencies that noted increased enforcement and public awareness campaigns. The research team found no significant difference in effects between white incandescent and blue light-emitting diode (LED) indicators.

For total, fatal and injury, and right-angle crashes, RLILs appeared to be more effective in rural areas and at intersections with lower total entering volume and a lower proportion of entering traffic from the minor road. The data indicated that the opposite was true for disobeyed signal crashes; the research team found RLILs were more effective in urban areas and at intersections with higher total entering volume and a higher proportion of entering traffic from the minor road. Owing to correlations among these factors, the disaggregate effects should not be combined for quantitative analysis; however, the indications can be considered when prioritizing intersections for treatment.

The B/C ratio estimated with conservative cost and service life assumptions and considering the benefits for total crashes was 92:1 for all signalized intersections. With the recommended U.S. Department of Transportation (USDOT) sensitivity analysis, this value could range from 53:1 to 130:1. These results suggest that the strategy—even with conservative assumptions on cost, service life, and the value of a statistical life—can be highly cost effective.

In addition to the crash-related benefits, RLILs can improve the efficiency and safety of red-light running enforcement efforts. While this study did not evaluate the efficiency and safety impacts with respect to enforcement, it is important to note that RLILs do allow police to observe violators from a downstream position, eliminating the need for a second observer (upstream) and the need to pursue a violator through the intersection during the red interval.

 

 

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