The effect of ambient noise within a vehicle on the audibility of safety sirens

Abstract

Driver response times to safety vehicle sirens can make the difference between life and death. Unfortunately, siren audibility is impeded by additional auditory stimuli (such as music), which more than 90% of drivers listen to. To better understand siren effectiveness in alerting drivers, ambient noise (including such additional stimuli) is measured with respect to a typical sedan to understand masking. Quantifying the sound propagation characteristics, specifically diffraction and attenuation, of sirens at set distances is done by measuring the A-weighted sound pressure levels outside and inside the sedan. Measurements are taken to simulate an emergency vehicle approaching from behind. Initial findings demonstrate that dBA levels are reduced more than two-fold when propagating inside a sedan with all noise sources off (engine, etc.). Ambient noise is studied in multiple designs, including engine idling or driving, and music at various sound pressure levels. This enables quantifying human detection thresholds to determine minimal masking values in various types/levels of ambient noise. Human detection thresholds are determined using established signal-to-noise ratio standards. Findings shall be discussed in terms of siren effectiveness in alerting drivers in the presence of ambient noise to provide insights to further the safety of the public and emergency personnel.