Research indicates that an emergency vehicle traveling faster than what speed might not be heard by bystanders?

Research highlights that an emergency vehicle traveling faster than 50 mph may not be heard by bystanders. This is primarily due to the physics of sound and the dynamics of speed. As the vehicle accelerates, the sound waves produced by the sirens struggle to catch up to the moving vehicle, diminishing their audibility to people in the vicinity. At speeds exceeding 50 mph, the combination of wind noise and increasing distance further reduces the likelihood that bystanders will hear the warning signals in time to react appropriately. This underscores the importance of traffic laws and operational protocols that aim to balance the need for speed during emergencies with the necessity of maintaining situational awareness among the public.