Rear-end collisions are, probably, the most common type of auto accident in the US. Ever wonder why? Because drivers do not leave enough distance between the front of their car and the back of the car in front of them. Plain and simple.
There’s an easy way to remedy that problem and make yourself virtually incapable of causing a rear-end collision—always maintain a safe braking distance.
Factors Affecting Braking Distance
How much distance it takes to actually stop your car depends on four factors:
- Your perception time—how long it takes you to realize that you need to slow down or come to a complete stop
- Your reaction time—how long it takes between the realization that you need to slow down/stop and actually move your foot from the accelerator to the brake pedal
- Vehicle reaction time—how long it takes from initial application of pressure on the brake pedal before your brakes engage
- Vehicle braking capability—how long it takes your car to fully stop once brakes are engaged
Consider these factors for just a moment and you’ll quickly realize why braking distance is so complicated and important:
- Braking starts with you. You have to know you need to brake. If you’re distracted, this realization is late in coming, and that cuts the distance you have to stop between you and the object you need to avoid hitting.
- Braking distance increases as brake health decreases. In other words, worn pads and rotors mean it’s going to take your car longer to stop.
- Braking distance is a function of speed. The faster you’re going, the longer it’s going to take to bring your car to a complete stop.
Remember, these are factors affecting your braking distance. The same applies to every other driver on the road, but you don’t get to control their focus, their brake maintenance or their speed. So, that means you may need to allow extra distance to accommodate for someone else’s slow reaction time.
Calculating Braking Distance
Braking distance is measured in feet/second. Average braking distance is calculated like this:
Distance traveled during perception/reaction time + distance travelled during deceleration
Assume you’re going 30 mph. Average perception/reaction time is 1.5 seconds, which translates to a distance traveled of 66 feet. Now, assuming your car has good brakes, at 30 mph, actual stopping distance required averages 45 feet. That’s a total stopping distance of 111 feet.
Take a look at what happens when you increase speed. At 60 mph:
- Perception and reaction time of 1.5 seconds results in a traveled distance of at least 132 feet.
- Actual stopping distance required averages 180 feet.
Total stopping distance at 60 mph is 312 feet. So, by increasing speed by 30 mph, you nearly triple the total stopping distance.
Eyeballing Braking Distance
Hopefully even all the math-o-phobes out there are still with us because leaving enough braking distance does not actually involve algebra. You simply have to count.
Because braking distance is a function of time, you need to leave enough time between you and the car(s) in front of you. And you can determine if there’s sufficient time/distance this way:
- Identify an upcoming landmark that you and the cars in front of you will pass, like a mile marker or signpost.
- Observe when the car in front of you passes the landmark.
- As soon as the car in front of you clears the landmark, start counting (saying “one-Mississippi, two Mississippi, etc. at a natural speaking pace can make your counting match actual clocked seconds).
- Stop counting when the front of your car reaches the landmark.
If your count is under three seconds, there is not enough braking distances…slow down!
Yes, at higher speeds, “enough” braking distance is going to mean there’s a lot of open road between you and the rear bumper of the car in front of you. Get used to seeing that. That open road space is what may save your life or spare you expensive collision repair damage some day.