Front line service workers in the transportation, construction, utility and delivery sectors of the work force are over-represented in terms of work place fatalities. Flashing yellow warning beacons often are the only line of defence between these workers and drivers on the road. Standards for warning beacons include specifications for minimum intensity characteristics to ensure visual detection, for chromaticity to ensure that they can be distinguished from red and blue emergency vehicle flashing lights, and for the flash rate to ensure conspicuity and to prevent seizures among drivers with photosensitive epilepsy. Previous research has suggested that if warning beacons are too bright under nighttime viewing conditions, they could produce glare. Prior studies have also shown that it can be difficult to judge closing distance when lights flash in an on-off pattern compared to temporally modulating lights that do not go completely off. The results of two experiments of visual responses to warning lights are summarized. These findings can enhance the foundations for warning beacon standards.
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