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2.6 – Controlling Speed
Driving too fast is a major cause of fatal crashes. You must adjust your speed depending on driving conditions. These include traction, curves, visibility, traffic and hills.
2.6.1 – Stopping Distance
Perception Distance + Reaction Distance + Braking Distance = Total Stopping Distance
Perception Distance. The distance your vehicle travels, in ideal conditions, from the time your eyes see a hazard until your brain recognizes it. Keep in mind, certain mental and physical conditions can affect your perception distance. It can be affected greatly depending on visibility and the hazard itself. The average perception time for an alert driver is 1 3/4 seconds. At 55 mph, this accounts for 142 feet traveled.
Reaction Distance. The distance you will continue to travel, in ideal conditions; before you physically hit the brakes in response to a hazard seen ahead. The average driver has a reaction time of three-fourths second to one second. At 55 mph this accounts for 61 feet traveled.
Braking Distance. The distance your vehicle will travel, in ideal conditions, while you are braking. At 55 mph on dry pavement with good brakes, it can take about 216 feet.
Total Stopping Distance. The total minimum distance your vehicle has traveled, in ideal conditions, with everything considered (including perception distance, reaction distance and braking distance) until you can bring your vehicle to a complete stop. At 55 mph, your vehicle will travel a minimum of 419 feet.
The Effect of Speed on Stopping Distance. The faster you drive, the greater the impact or striking power of your vehicle. When you double your speed from 20 to 40 mph, the impact is four times greater. The braking distance is also four times longer. Triple the speed from 20 to 60 mph and the impact and braking distance is nine times greater. At 60 mph, your stopping distance is greater than the length of a football field. Increase the speed to 80 mph and the impact and braking distance are 16 times greater than at 20 mph. High speeds greatly increase the severity of crashes and stopping distances. By slowing down, you can reduce braking distance.
The Effect of Vehicle Weight on Stopping Distance. The heavier the vehicle, the more work the brakes must do to stop it and the more heat they absorb. The brakes, tires, springs and shock absorbers on heavy vehicles are designed to work best when the vehicle is fully loaded. Empty trucks require greater stopping distances because an empty vehicle has less traction.
Multiple-Choice Questions:
Define "Braking Distance":
- The total minimum distance your vehicle has traveled, in ideal conditions, with everything considered, until you can bring your vehicle to a complete stop.
- The distance your vehicle travels, in ideal conditions, from the time your eyes see a hazard until your brain recognizes it.
- The distance your vehicle will travel in ideal conditions, while you are braking.
- The distance you will continue to travel, in ideal conditions; before you physically hit the brakes in response to a hazard seen ahead.
Braking Distance. The distance your vehicle will travel, in ideal conditions, while you are braking. At 55 mph on dry pavement with good brakes, it can take about 216 feet.
Define "Total Stopping Distance":
- The total minimum distance your vehicle has traveled, in ideal conditions, with everything considered, until you can bring your vehicle to a complete stop.
- The distance you will continue to travel, in ideal conditions; before you physically hit the brakes in response to a hazard seen ahead
- The distance your vehicle will travel in ideal conditions, while you are braking.
- The distance your vehicle travels, in ideal conditions, from the time your eyes see a hazard until your brain recognizes it.
Total Stopping Distance. The total minimum distance your vehicle has traveled, in ideal conditions, with everything considered (including perception distance, reaction distance and braking distance) until you can bring your vehicle to a complete stop. At 55 mph, your vehicle will travel a minimum of 419 feet.
Why do empty trucks sometimes require a greater stopping distance than loaded trucks?
- Only the trailer brakes are activated when the truck is empty or very light
- They designed the brakes with a delay for lighter loads
- Antilock brakes are disabled when the total weight of the vehicle is below a certain amount
- An empty vehicle has less traction
When you double your speed from 20 to 40 mph, the impact on "total stopping distance" and "braking distance" is:
- The impact is barely noticeable
- Two times greater
- Four times greater
- Eight times greater
The Effect of Speed on Stopping Distance. The faster you drive, the greater the impact or striking power of your vehicle. When you double your speed from 20 to 40 mph, the impact is four times greater. The braking distance is also four times longer.
Define "Reaction Distance":
- The total minimum distance your vehicle has traveled, in ideal conditions, with everything considered, until you can bring your vehicle to a complete stop.
- The distance you will continue to travel, in ideal conditions; before you physically hit the brakes in response to a hazard seen ahead
- The distance your vehicle travels, in ideal conditions, from the time your eyes see a hazard until your brain recognizes it.
- The distance your vehicle will travel in ideal conditions, while you are braking.
Reaction Distance. The distance you will continue to travel, in ideal conditions; before you physically hit the brakes in response to a hazard seen ahead. The average driver has a reaction time of three-fourths second to one second. At 55 mph this accounts for 61 feet traveled.
Perception Distance + Reaction Distance + Braking Distance =
- Total slowing distance
- Total Stopping Distance
- Total momentum
- Braking resistance
Perception Distance + Reaction Distance + Braking Distance = Total Stopping Distance
Total Stopping Distance. The total minimum distance your vehicle has traveled, in ideal conditions, with everything considered (including perception distance, reaction distance, and braking distance) until you can bring your vehicle to a complete stop. At 55 mph, your vehicle will travel a minimum of 419 feet.
When measuring the "total stopping distance" at 55 mph, your vehicle will travel a minimum of how far?
- 216 feet
- 300 feet
- 419 feet
- 142 feet
Total Stopping Distance. The total minimum distance your vehicle has traveled, in ideal conditions, with everything considered (including perception distance, reaction distance and braking distance) until you can bring your vehicle to a complete stop. At 55 mph, your vehicle will travel a minimum of 419 feet.
Define "Perception Distance":
- The distance you will continue to travel, in ideal conditions; before you physically hit the brakes in response to a hazard seen ahead.
- The total minimum distance your vehicle has traveled, in ideal conditions, with everything considered, until you can bring your vehicle to a complete stop.
- The distance your vehicle travels, in ideal conditions, from the time your eyes see a hazard until your brain recognizes it.
- The distance your vehicle will travel in ideal conditions, while you are braking.
Perception Distance. The distance your vehicle travels, in ideal conditions, from the time your eyes see a hazard until your brain recognizes it. Keep in mind, certain mental and physical conditions can affect your perception distance. It can be affected greatly depending on visibility and the hazard itself. The average perception time for an alert driver is 1 3/4 seconds. At 55 mph, this accounts for 142 feet traveled.
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