Warning Light Flash Frequency as a Method for Visual Communication to Drivers

Abstract

Service vehicles use flashing warning lights to indicate their presence to approaching drivers. Present standards offer ranges of flash frequencies to enhance conspicuity and avoid potential risks of photosensitive epilepsy or other issues. But, in practice, the flash frequency is not varied in specific situations. Previous studies have indicated that people interpret faster flash frequencies as more “urgent” than slower flash frequencies. Building on these findings, a laboratory study was conducted to identify whether drivers might be able to use cues from the frequency of flashing warning lights to anticipate how a service vehicle might behave in a work zone or other incident scene. The results suggest that even if they are not taught about the interpretation of different flash frequencies, drivers can differentiate between 1 Hz and 4 Hz flashing lights and learn to make accurate predictions about their meaning. The results also indicate that there are no reliable differences between 1 Hz and 4 Hz flashing in relation to a driver’s ability to detect when a service vehicle has begun to move. Based on the results, a preliminary suggestion is made to use lights flashing at 1 Hz when a service vehicle is moving forward, and 4 Hz when it is traveling in reverse.