Determining optimum flash patterns for emergency service vehicles: An experimental investigation using high definition film

• The 4 Hz flash rate was perceived to convey greater urgency than 1 Hz rate.
• The 1 Hz single pulse pattern was ranked least urgent of all the combinations.
• Estimates of minimum space acceptable for ‘pulling out’ reflected urgency measures.
• Less risky gap acceptance judgements were evident for the 4 Hz single pulse combination.
• HD film was found to be a low-risk, valid method for assessing EVL efficacy.

An investigation of how emergency vehicle lighting (EVL) can be improved is reported with reference to an analysis of police vehicle road traffic accidents (Study 1). In Study 2, 37 regular drivers were shown film clips of a marked police vehicle, in which flash rate (1 Hz, 4 Hz) and pattern (single, triple pulse) were varied on the blue Light Emitting Diode (LED) roofbar. Results indicate a 4 Hz flash rate conveys greater urgency than a 1 Hz rate, while a 1 Hz, single flash combination was ranked the least urgent of all combinations. Participants claimed they would leave significantly more space before pulling out in front of an approaching police car (gap acceptance) in the 4 Hz single pulse condition in comparison to other EVL combinations. The preliminary implications for which flash characteristics could prove most optimal for emergency service use are discussed with regard to effects on driver perception and expected driving behaviour.