Speed and Stopping Distances

To stop safely, you must be able to calculate a safe speed based on the distance needed to stop.

• Safe speed is necessary to control your vehicle and stop in time to avoid a collision.
• The greater the speed, the greater the stopping distance.
• To determine a safe speed, you must understand stopping distances and how to factor in sight distance and reaction time.

Sight Distance

• Sight distance means the distance from which you can see and identify a hazard. You often see an object before you're able to identify it as a hazard.
• If the stopping distance to an object is greater than the sight distance, you're in danger of hitting the object.

Reaction Time and Distance

• Reaction time is the time it takes you to react to a hazard. It involves these steps:
  • Seeing something
  • Recognizing it's a hazard
  • Deciding whether to brake or steer around the object
  • Reacting
• Reaction distance is the distance the ATV travels during your reaction time.
  • The distance depends on the reaction time (in seconds) and speed (in feet per second).
  • It is calculated as: Reaction Distance = Reaction Time x Speed
• Accidents occur in just a few seconds, so think of your speed in feet per second (multiply mph by 1.46667).
  • 15 mph = 22 ft. per second
  • 30 mph = 44 ft. per second
  • 45 mph = 66 ft. per second
  • 60 mph = 88 ft. per second
• At 30 mph with a reaction time of three seconds, the reaction distance is 132 feet (3 sec. x 44 ft./sec.).

Braking Distance

• Braking distance is the distance traveled while you're braking to a stop. It depends on two factors: speed and drag.
• Drag is the amount of friction between the tires and the surface of the terrain. For example, mud has more drag than dirt. A hard, dry surface has more drag than a hard, wet surface; and ice has very little drag.

Total Stopping Distance Formula

Stopping Distance = Reaction Distance + Braking Distance

Normal Reaction Time

Studies reflect that a person's reaction time is anywhere from one to three seconds. In general, however, three seconds is probably more accurate.