Stopping at 60 mph takes _____ that it takes at 30 mph.

Stopping at 60 mph takes over three times the distance that it takes at 30 mph. The stopping distance is the sum of the perception distance (how far your vehicle travels until your brain notices a hazard), the reaction distance (how far your vehicle travels until your brain moves your foot to the brake pedal and starts to brake), and the braking distance (how far your vehicle travels until the brakes bring it to a stop). Of these distances, only the braking distance is proportional to the square of the speed. That is, the braking distance at 60 mph is about four times the braking distance at 30 mph. [Adjusting Speed, Safe Driving Tips, South Dakota Driver License Manual]