There are three things that add up to total stopping distance:
Perception Distance + Reaction Distance +
Braking Distance = Total Stopping Distance
• Perception distance.
This is the distance your vehicle travels from the time your eyes
see a hazard until your brain recognizes it. The perception time
for an alert driver is about 3/4 second. At 55 mph, you travel 60
feet in 3/4 second.
• Reaction distance.
The distance traveled from the time your brain tells your foot
to move from the accelerator until your foot is actually pushing
the brake pedal. The average driver has a reaction time of 3/4 second.
This accounts for an additional 60 feet traveled at 55 mph.
• Braking distance.
The distance it takes to stop once the brakes are put on. At 55
mph on dry pavement with good brakes it can take a heavy vehicle
about 170 feet to stop. It takes about 4 1/2 seconds.
• Total stopping distance.
At 55 mph it will take about 6 seconds to stop and your vehicle
will travel about the distance of a football field. (60 + 60 + 170
= 290 feet).
The Effect of Speed on Stopping Distance.
Matching Speed to the Road
Identifying Slippery Surfaces.
Speed and Curves
Speed and Distance Ahead
Speed and Traffic Flow
Speed on Downgrades