The speed of your car affects the distance required to stop it. Stopping
distance is determined by three factors:
- Perception distance. This is the length a vehicle travels from the time
you see a hazard until your brain recognizes it. For an alert driver, this
is approximately ¾ of a second.
- Reaction distance. This is the length a vehicle travels in the time it
takes your brain to tell the foot to move from the gas pedal to the brake
pedal and apply pressure. This takes approximately ¾ of a second.
- Braking distance. This is the length it takes to stop a vehicle once
the brakes are applied.
Here's some food for thought. At 55 mph, your vehicle is traveling at
about 80 feet per second. Feet-per-second is determined by multiplying
speed in miles-per-hour by 1.47 (55 mph x 1.47 = 80 feet per second.)
With this in mind, let's add the perception and reaction distance to the
formula.
You're traveling at 80 feet per second and you see a hazard in the road
ahead. It takes about ¾ of a second for your brain to acknowledge the
hazard. During this fraction of a second, you've traveled an additional
60 feet. This is the perception distance.
Now that your brain has acknowledged the hazard ahead, it takes another
¾ of a second for it to tell the foot to move from the gas pedal to the
brake pedal and apply pressure. During this reaction time, you've traveled
another 60 feet.
So from the time you perceive the hazard until the time your foot is
applying pressure to the brake pedal, you've traveled 120 feet but your
car still isn't stopped. At 55 mph, on a dry road with good brakes, your
vehicle will skid approximately 170 feet more before stopping. This
distance, combined with the perception and reaction distances, means you
need about 300 feet to stop a car traveling at 55 mph. As a point of
reference, Lambeau Field is 360 feet long, end to end. Keep this in mind
as you follow that other car on your way home tonight.
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