What is reaction time when driving?

The definition of reaction time, in terms of driving, is how long it takes you to react to an emergency: by hitting the brakes, turning the wheel, etc.

For most people, this time is approximately 1 second, which at a speed of 60 mph is about 90 feet. So if the emergency occurs within that distance, you probably won't have had time to avoid the accident.

Many insurance companies, however, use a much stricter standard of 1.5 seconds (135 feet), this being (on average) the amount of time it takes to recognize an emergency, decide upon an action, and then execute it.

This is one reason why you're supposed to keep a minimum of four car lengths (2 seconds) between you and the car you're following while at freeway speeds.