Stopping Distance: Summary

Total stopping distance is reaction distance plus braking distance. So, from 60 mph, reaction takes 66 feet and braking takes 130 feet, for a total of 196 feet. Total elapsed time is 3.7 seconds (0.75 seconds reaction, plus 2.95 seconds to brake).

The calculations reveal why attentiveness, physical capability, and skill are so important to safe driving. Reaction time can easily double from 0.75 seconds to 1.5 seconds (neither one is very long), with just the slightest distraction, adding another 66 feet to total stopping distance. The deceleration rate depends on the skill of the driver to apply maximum pressure on the brake pedal without skidding and maintaining it throughout the stop (or properly using ABS brakes), and also on rarely ideal conditions, recognizing that few circumstances other than driving uphill make braking distance shorter than the best case. If the deceleration rate is 20 feet per second per second rather than 30, the stopping distance increases from 130 to 195 feet. The problem with ABS brakes is that we often release pressure on the pedal when it begins to pulsate, negating the benefits of the anti-lock function - the rule is hit 'em hard and stay on 'em.

If you see differences in reported stopping distances, those typically result from differences in the assumed reaction time and the deceleration rate that is used in the calculations, since the other components of the calculations are constants or reasonable approximations. There seems to be better general agreement on the reaction time than the deceleration rate.

Or, instead of all this you can just memorize that 60 mph's stopping distance is 200 feet. It's more if you are going faster and less if you are going slower. Close enough for a multiple choice test, anyway.