What factor can prevent motorists from hearing a siren in time?

High speeds can significantly prevent motorists from hearing a siren in time due to the increased noise generated by the vehicle itself. At higher speeds, the sound of the engine, tires on the roadway, and wind resistance create a louder environment inside the car, which can drown out external noises, including the sound of emergency vehicle sirens. Additionally, as a vehicle moves faster, the time taken to react to sounds decreases, thereby limiting the ability of the motorist to respond to the siren promptly.

In contrast, while time of day, type of roadway, and weather conditions can also influence a motorist's ability to hear, they do not directly relate to the immediate impact of speed on sound perception and reaction time in the same way high speeds do.