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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations

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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

Chapter 1. Introduction

This chapter presents background information on the installation of RLILs at traffic signals. It also provides a brief overview of the ELCSI-PFS, of which the study reported here is a part, and the literature review conducted for this study.

Background on Strategy

This strategy involves installing RLILs—also known as signal indicator lights, enforcement lights, rat lights or boxes, or tattletale lights—at traffic signals. RLILs can be mounted on the signal head, as shown in Figure 1 , or on the mast arm. The indicator activates simultaneously with the red interval, allowing an enforcement officer downstream to identify whether a vehicle has violated the red interval. While the lights should be visible for the enforcement officer to more safely conduct enforcement operations, the lights should be designed such that they do not confuse drivers (i.e., they should not be red, yellow, or green).

This photo shows a red-light indicator light mounted on a signal head. The bulb connected to the top of the signal head with a support. The signal is in the red phase and the red-light indicator light is activated.


Figure 1 . Photo. RLIL on signal head.

In its series of reports on innovative intersection safety treatments, FHWA presented a summary on enforcement lights.(1) The summary states that compared with other enforcement methods, enforcement lights can provide safety, efficiency, and/or cost benefits, including the following:

The FHWA summary also includes several implementation considerations. Because RLILs are not traffic-control devices, there are no compliance issues with the Manual on Uniform Traffic Control Devices for Streets and Highways.(2) However, it is worthwhile to consider the following points regarding implementation:

Background on Study

In 1997, the American Association of State Highway and Transportation Officials Standing Committee on Highway Traffic Safety, with the assistance of FHWA, the National Highway Traffic Safety Administration, and the Transportation Research Board Committee on Transportation Safety Management, met with safety experts in the field of driver, vehicle, and highway issues from various organizations to develop a strategic plan for highway safety. These participants developed 22 key emphasis areas that affect highway safety.(3)

The National Cooperative Highway Research Program published a series of guides to advance the implementation of countermeasures targeted to reduce crashes and injuries. Each guide addresses one of the emphasis areas and includes an introduction to the problem, a list of objectives for improving safety, and strategies for each objective. The guides designate each strategy as proven, tried, or experimental. For many of the strategies discussed in these guides, no States or agencies have performed evaluations; the guides consider about 80 percent of the strategies tried or experimental.

In 2005, to support the implementation of the guides, FHWA organized a pooled fund study of States to evaluate low-cost safety strategies as part of this strategic highway safety effort. Over the years, the pooled fund has grown in size and now includes 40 States. The purpose of the ELCSI-PFS is to evaluate the safety effectiveness of high priority tried and experimental low-cost safety strategies selected by member States through scientifically rigorous crash-based studies. The use of RLILs was selected as a strategy to be evaluated as part of this effort.

The ELCSI‐PFS conducts its research within the FHWA’s DCMF program, which is a comprehensive, long‐term safety research effort. FHWA established the DCMF program in November 2012 to support and complement the efforts of the ELCSI-PFS. The ultimate goal of the DCMF program is to save lives by identifying new safety countermeasures that effectively reduce crashes and promoting those countermeasures for nationwide installation by providing measures of their safety effectiveness, including B/C ratios, through research.

Literature Review

Reddy et al. conducted the leading study to date, examining the effectiveness of white enforcement lights in Hillsborough County, FL.(4) They noted that white enforcement lights allowed police officers to operate more effectively because the required manpower could be cut in half. Prior to installation, it took two officers to enforce red lights (one upstream to observe the red light and the other downstream to stop the offending driver). Reddy et al. evaluated 17 signalized intersections in Hillsborough County to determine the effectiveness of white lights in reducing red-light violations and associated crashes. They observed red-light violations in the a.m. and p.m. peak hours for 5 months prior to installation and 3 months after installation. In addition, they collected crash data from 2000 to 2005 from the Florida Department of Transportation (FDOT) Crash Analysis Reporting (CAR) system.(4)

A review of the crash data indicated an average of 828 crashes per year at the treatment sites before treatment and 860 crashes per year after treatment. Further analysis determined an average of 56 disregarded traffic signal crashes per year in the before period and 52 crashes per year in the after period. Considering only the approaches with white lights, red-light running crashes decreased from 40.17 crashes per year to 28 crashes per year after treatment. The authors noted an increase in all crashes countywide during the study period, while the trend in red-light running crashes stopped increasing in 2002, the year that white light installation began.(4)

The number of red-light running citations increased from 17,561 per year before treatment to 24,551 per year after treatment. The researchers documented that police officers found the white lights made the task of red-light enforcement simpler and safer. The red-light violation data collected at the study intersections showed a statistically significant reduction at the 90-percent confidence level in violations from 759 to 567 after white light installation. Owing to high variation, the results from the analyses of crash data were less conclusive than the results of the violation data.(4)



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