Evaluation of the Use of Strobe Lights in the Red Lens of Traffic Signals

About the report:

The objective of this study was to evaluate the effectiveness of using strobe lights in the red lens of traffic signals and, if appropriate, to recommend guidelines for their use. Strobe lights are used as a supplement to the red lens to draw the attention of drivers to a traffic signal. VDOT has 22 intersections with strobe lights in six of its nine districts; this is up from 3 intersections in 1987. Nineteen of these are in the western part of the state, and most have the strobe light in the red signal over the left through lane. The Barlo strobe light, a horizontal bar positioned across the middle of the red lens with about 60 flashes of white light per minute, is used at all 22 intersections. The cost of a red signal head with a Barlo strobe light is about $765. Strobe lights are used by VDOT primarily for (1) areas with a high truck volume and high speed; (2) areas with a high accident rate; (3) areas with road geometrics, especially grades (downgrade), horizontal curves, and other features, that result in limited sight distance; and (4) isolated intersections where a signal is unexpected. Based on the analyses, there was no evidence indicating that strobe lights are consistently effective in reducing accidents. The limitations of the analyses are identified in the study. There is no basis for recommending the use of strobe lights unless there are other bona fide measures of effectiveness that can be used to justify installing them.

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