Responses to Flashing Warning Lights and Colors of Service Vehicles

Flashing warning lights and vehicle markings of various colors are used on a wide range of emergency and other service vehicles to help inform drivers about the presence of these vehicles and the types of situations that drivers are approaching. Although not applied consistently among all jurisdictions, the colors and performance of these visual elements are often selected to help communicate the type of scenario (such as red flashing lights to indicate an emergency vehicle, or yellow flashing lights to indicate a non-emergency service vehicle). Previous investigations have shown that flashing light colors, vehicle and marking colors, and flashing temporal characteristics (e.g., rapid versus slower flashing) can all affect a driver’s perception of whether a vehicle along the road is responding to an emergency situation or not. Building on previous research, a laboratory study was carried out to investigate how drivers perceive scale-model roadway scenarios including different numbers of vehicles varying in their colors, and with flashing lights modulating at different intensity levels and flash frequencies. For each scenario, observers were asked whether as drivers they would proceed with caution past the scene or prepare to slow down or stop. Observers’ responses were recorded, and the time taken to provide a response was also recorded as a measure of certainty/uncertainty. Overall, the results show that coordinating the presence and color of flashing lights with the colors of vehicles and their markings are among the primary cues used by drivers to assess whether a roadside incident scene is an emergency situation or not. The results also provide suggestions for using flashing lights when multiple vehicles are present to reinforce consistent judgments among drivers.