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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 9. Summary and Conclusions

The objective of this study was to undertake a rigorous before–after evaluation of the safety effectiveness of RLILs as measured by crash frequency. The study used data from Florida to examine the effects on specific crash types, including total, fatal and injury, right-angle, left-turn, rear-end, nighttime, and disobeyed signal crashes. Based on the combined results, the research team recommends the CMFs shown in table 18 for the various crash types.

Table 18 . Results of Florida


Crash Type


Fatal and Injury




Disobey Signal


Estimate of CMF








SE of estimate of CMF








Note: Boldface indicates CMF estimates that are statistically significant at the 95-percent confidence level.

A disaggregate analysis of the results indicated that RLILs were almost immediately effective, and the effect was sustained for disobeyed signal crashes. For other crash types, CMFs decreased over the first few years of treatment, indicating that they were more effective for reducing crashes as drivers became accustomed to them. The smallest CMFs were for the only district with agencies that noted enforcement and public awareness campaigns. There was no indication of a notable increase in the level of enforcement. There were consistent reports that enforcement was based on intersections with high crash counts and that it was not focused on intersections with red-light indicators only. Some agencies focused awareness campaigns on the indicator lights, while others focused on red-light running in general. The research team found no significant difference between indicator types used.

In addition, RLILs appeared to be more effective for total, fatal and injury, and right-angle crashes in rural areas at signalized intersections with lower total entering volume and a lower proportion of entering traffic from the minor road. The research team found the opposite was true for disobeyed signal crashes, where RLILs appeared to be more effective in urban areas at signalized intersections with higher total entering volume and a higher proportion of entering traffic from the minor road. The analysis showed that one should not combine these factors for quantitative analysis but can consider them 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 USDOT recommended 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 cost effective.



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