What does reaction distance measure?

Reaction distance specifically refers to the distance a vehicle travels while the driver recognizes a hazard and initiates a response to it. This process involves the brain receiving signals about a need to brake—essentially the time taken from when an event is perceived to when the action (such as pressing the brake pedal) begins.

This measurement is crucial for understanding stopping distances and the importance of a driver’s alertness and readiness, as any delay in response can result in additional distance traveled, increasing the risk of an accident.

While other distances, such as braking distance, concern how far a vehicle travels after the brakes are applied, reaction distance specifically isolates the moment from hazard recognition to the first action taken in response.