Animation: Speed and Stopping Distances
Animation Transcript
Transcript for Speed and Stopping Distances
A person is riding a snowmobile in the sitting position.
Stopping a snowmobile is trickier than stopping a wheeled vehicle on a street or a trail. To ensure that you can stop safely in any situation, you must be able to calculate a safe speed based on stopping distances.
Safe Speed
- Maintaining a safe speed allows you to control your machine and stop in time to avoid a collision.
- The greater the speed, the greater the stopping distance.
- To determine a safe speed, you must know stopping distances and how to factor in sight distance and reaction time.
Sight Distance
The scene zooms out to show the path ahead of the person.
- Sight distance is the distance from which you can see and identify a hazard, not necessarily the total distance you can see. 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
The scene again zooms in to show the person riding the snowmobile.
Reacting to a sudden need to stop involves these steps.
- Seeing something
- Recognizing it is a hazard
- Deciding what to do (A question mark appears and then disappears.)
- Braking or steering around the object
Reaction Time Distance
- Reaction time distance is the distance the snowmobile travels during the time it takes you to react.
- The distance is calculated by multiplying reaction time (in seconds) by speed (in feet per second).
Reaction Time Distance = [Reaction Time] × [Speed]
The graph showing stopping distances for snowmobiles is shown.
Speed in Feet Per Second
- 15 mph = 22 ft. per second
- 30 mph = 44 ft. per second
- 45 mph = 66 ft. per second
- 60 mph = 88 ft. per second
Stopping Distance
Stopping distance is the sum of the reaction time distance plus the braking distance.
Stopping Distance = Reaction Time Distance + Braking Distance
Braking Distance
- Braking distance is the distance traveled after you apply the brakes.
- Braking distance depends on two factors: speed and drag.
Drag Factors
- The drag factor is a measure of the friction between the snowmobile’s track and the surface it travels over.
- Deep, powdery snow stops snowmobiles more quickly because it creates more drag than shallower snow.
- Glare ice has less drag than deep snow, so snowmobiles travel much farther after braking.