Evaluation of the use of strobe lights in the red lens of traffic signals : technical assistance report.

Cottrell, B.H., Jr · 1994 · ROSA P / Virginia Transportation Research Council (VTRC)

archive: archived pipeline: cataloged verified

Get this paper ↗ (full text — opens at the source; we link to it, we don't host it)

Summary

This technical assistance report evaluates the effectiveness of strobe lights installed in the red lenses of traffic signals, specifically the Barlo strobe light, which flashes approximately 60 times per minute. The study was motivated by the increasing popularity of these devices within the Virginia Department of Transportation (VDOT), which expanded from three intersections in 1987 to 22 in 1994, despite a lack of conclusive evidence regarding their safety benefits. The primary objective was to determine if strobe lights consistently reduce accidents and to establish guidelines for their use, particularly in areas with high truck volumes, high speeds, limited sight distance, or unexpected signal locations. The research methodology involved two main components: a survey of VDOT district traffic engineers and a statistical analysis of accident data. The survey gathered information on installation locations, maintenance experiences, and reasons for deployment. For the quantitative analysis, the researchers selected six intersections with strobe lights that had at least three years of accident data before and after installation. The evaluation employed three analytical approaches: a review of accident trends, a before-and-after analysis using the Z test, and a more rigorous before-and-after analysis with a comparison group to control for regression toward the mean. The study examined rear-end, angle, and total accidents involving vehicles on the strobe-light approaches. The findings indicated no statistical evidence that strobe lights effectively reduced accidents. In the trend analysis, accident rates remained unchanged or increased at several sites, with some showing increases of over 100 percent for rear-end collisions. The Z test revealed no significant effect on rear-end or angle accidents and suggested a harmful effect on total accidents at two sites. The comparison group analysis also failed to demonstrate effectiveness, partly because treatment and comparison sites were often not statistically comparable due to the non-random selection of strobe light locations. The study noted limitations, including the inability to verify if accidents occurred while the strobe was flashing and the low statistical power due to small sample sizes. The report concludes that there is no basis for recommending the use of strobe lights for safety improvement, as they do not consistently reduce accidents. The authors suggest that driver noncompliance and willful disregard for signals may limit the devices' effectiveness. Consequently, the findings can justify the removal of existing strobe lights. The report recommends alternative measures, such as signal-ahead warning signs with hazard identification beacons or back-plates to increase signal visibility, for the conditions where strobe lights are currently deployed. While VDOT may continue installations due to public requests or engineering judgment, the study asserts that strobe lights should only be used if other bona fide measures of effectiveness can justify their cost and presence.

Key finding

There is no statistical evidence that strobe lights in red traffic signal lenses are effective in reducing accidents.

Methodology

field_study

Sample size: 6

Provenance

The full processing record for this entry. Every stage of this paper's journey through the pipeline is logged — what ran, with which tool and model, how many attempts it took, and when it last completed. Discovered via bulk_ingest_rosap on 2026-05-23 (6 acquisition events logged).

Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

Topics

Ranked by relevance to this paper. Hover a topic for its definition.

• roadway lighting effects
• emergency work zone conspicuity