SPEED, IMPACT AND BRAKING DISTANCE It is a well-known fact that the faster you drive the greater the impact or striking power of  your vehicle. A fact not generally understood is how much greater the striking power of a  vehicle is when you double the speed from 20 to 40 miles per hour. It is commonly believed  that the striking power of a vehicle would likewise be doubled. This is not true. The impact  is 4 times greater at 40 mph than at 20 mph. The braking distance is also 4 times longer.  Triple the speed from 20 to 60 mph and the impact and braking distance are 9 times greater.  Increase the speed to 80 mph and the impact and braking distance are 16 times greater  than at 20 miles per hour.  Respect the potential destructive power of your vehicle when you increase speed. Speed  properly related to traffic, road, and weather conditions, and skillfully controlled by a  thoughtful driver need not be hazardous. In the hands of a thoughtless, uninformed driver it  is deadly.  NOTE:  While this chart recommends the use of the 4 second rule, 13 AAC 02.090 requires  at a minimum the 2 second rule.  20 29 22  24  44 33 54 59 44 96 74 55 146 88 66 215 103 77 290 TREE  TREE 1. Start counting “one thousand and one...” as vehicle aheadpassestree.  2. Your should count “one thousand and four” before reaching the tree.  MI.  PER  HR. FT.  PER  SEC. 46 ft. 87 ft. SPEED AND STOPPING DISTANCES Total minimum stopping distances  with perfect 4-wheel brakes on best  type of road surface under favorable  conditions 140 ft. 30 201 ft. 40 50 60 70 Thinking Distance 281 ft. Braking  Distance  367 ft. Four-second rule