How To Calculate Your Braking Distance

While you might not think of your braking distance every time you drive across town, you will eventually be very interested in slowing down as fast as possible. All sorts of things can go wrong, and highway driving is deceptively fast. Children can run into the road, animals can wander in front of you.... the possibilities are endless, and they're very real. Here's a few tips I've put together to help you understand what kind of braking distance you can expect and how speed affects your braking distance.

1. Braking Distance: "Braking distance" is the distance your car travels after the brakes have been applied. According to auto industry standards for deceleration, if you are traveling at 70 miles per hour, it takes 315 feet to stop an average car once the brakes have been applied.
2. Stopping Distance: The term "stopping distance" takes into account the distance you travel before you hit the brake (reaction distance) plus the distance you travel while the brakes slow you down (braking distance). This might not seem like a big difference, but if you're moving down an interstate highway at 70 mph, you're passing 100 feet of asphalt every second.
   
3. Reaction Distance: If it takes you 1.5 seconds to realize that a problem exists, you've already passed 150 feet. That means you've passed half a football field before the brakes have even begun to kick in. Since you and I probably agree that half a football field is a long time to travel before we start slowing down, we'll include reaction distance in the discussion.
4. Variables: Braking distance varies depending on many variables, including your reaction time, the speed at which you are traveling, the weight of the car, road conditions, braking efficiency, and friction between the surface of the road and your tires. You can see that there are many things that can go wrong when you need to brake in a hurry. That is why most traffic experts advise you to stay three to four seconds behind the car in front of you.
5. There are two times when you should be interested in calculating your braking distance.

   Road Test: You can determine your braking distance on a test track or empty parking lot. You need to set up cones or use a landmark to indicate the point at which you will begin braking. Bring a measuring tape or similar device to measure 10 ft intervals. When you're ready to test, test your braking distance at 10, 20, 30, and 40 miles per hour. Make sure nobody is nearby--it's best to avoid having a real emergency braking situation. For safety's sake, don't test your braking distance at higher speeds, and keep the car going straight until you are stopped.

   While driving: Since you probably aren't interested in calculating all of those numbers while you drive, you might prefer to recall the 3 second rule. Stay at least 3 seconds behind any car you are following so that you will have time to slow down. If road conditions are bad, you need to give yourself more room to slow down in case something happens.

6. If you're interested in calculating your braking distance using some math formulas, check out Distance Calculator.