Speed and Stopping Distances

• Stopping distance


  Made up of two components: thinking distance and braking distance
• Typical stopping distances


  • 30 mph: 9m thinking, 15m braking
  • 50 mph: 21m thinking, 38m braking
  • 70 mph: 24m thinking, 75m braking
• To avoid an accident, drivers need to leave enough space between their car and the one in front so that if they had to stop suddenly they would have time to do so safely
• Enough space means the stopping distance for whatever speed they're going at
• Bad weather and road conditions will make stopping distances even longer
• At 30 mph, you should drive no closer than 6 or 7 car lengths away from the car in front
• Speed limits are important because speed affects the stopping distance so much
• As a car speeds up

  Thinking distance increases at the same rate as speed
• Thinking time (how long it takes the driver to apply the brakes) stays pretty constant
• As speed doubles


  Braking distance increases 4-fold
• Stopping distance is a combination of thinking distance and braking distance
• The stopping distance for vehicle B is 7m longer than for vehicle A at 40mph