Dashboard

Dashboard

Note: Your are not logged in. We can not keep your scores or track your progress unless you Register and Log In

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:

Question #84 (1 of 8)

Give a brief explanation of the problem:

Optional: Leave your email address if you would like a reply:

Report Cancel

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.

Think about that for a minute. If you double the speed, you quadruple the stopping distance! That's huge. If you triple your speed, your stopping distance is nine times as long! Slow down, be safe.
Next
Question #81 (2 of 8)

Give a brief explanation of the problem:

Optional: Leave your email address if you would like a reply:

Report Cancel

Define "Braking 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 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 total minimum distance your vehicle has traveled, in ideal conditions, with everything considered, until you can bring your vehicle to a complete stop.

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.

Memorize this definition. You may see it on the test and you need to understand it.
Previous Next
Question #77 (3 of 8)

Give a brief explanation of the problem:

Optional: Leave your email address if you would like a reply:

Report Cancel

Perception Distance + Reaction Distance + Braking Distance =

  • Total momentum
  • Total Stopping Distance
  • Braking resistance
  • Total slowing distance

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.

Memorize this formula! It will almost certainly be on the written exam.
Previous Next
Question #85 (4 of 8)

Give a brief explanation of the problem:

Optional: Leave your email address if you would like a reply:

Report Cancel

Why do empty trucks sometimes require a greater stopping distance than loaded trucks?

  • 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
  • Only the trailer brakes are activated when the truck is empty or very light
  • An empty vehicle has less traction
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.
To be honest, I think this is true on very slick roads, but not necessarily on dry roads. On snow-covered or icy roads the brakes may overpower the grip you have, causing the tires to slide, which increases your stopping distance.
Previous Next
Question #78 (5 of 8)

Give a brief explanation of the problem:

Optional: Leave your email address if you would like a reply:

Report Cancel

Define "Reaction Distance":

  • The distance your vehicle travels, in ideal conditions, from the time your eyes see a hazard until your brain recognizes it.
  • 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 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.

Memorize this definition. You may see it on the test and you need to understand it.
Previous Next
Question #79 (6 of 8)

Give a brief explanation of the problem:

Optional: Leave your email address if you would like a reply:

Report Cancel

Define "Total Stopping Distance":

  • The distance your vehicle travels, in ideal conditions, from the time your eyes see a hazard until your brain recognizes it.
  • 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 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

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.

Memorize this definition. You may see it on the test and you need to understand it.
Previous Next
Question #82 (7 of 8)

Give a brief explanation of the problem:

Optional: Leave your email address if you would like a reply:

Report Cancel

Define "Perception Distance":

  • 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.
  • The total minimum distance your vehicle has traveled, in ideal conditions, with everything considered, until you can bring your vehicle to a complete stop.

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.

Memorize this definition. You may see it on the test and you need to understand it.
Previous Next
Question #83 (8 of 8)

Give a brief explanation of the problem:

Optional: Leave your email address if you would like a reply:

Report Cancel

When measuring the "total stopping distance" at 55 mph, your vehicle will travel a minimum of how far?

  • 300 feet
  • 216 feet
  • 142 feet
  • 419 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.

You may have to know this number for the test, so memorize it.
Previous Next

Why Join Trucking Truth?

We have an awesome set of tools that will help you understand the trucking industry and prepare for a great start to your trucking career. Not only that, but everything we offer here at TruckingTruth is 100% free - no strings attached! Sign up now and get instant access to our member's section:
High Road Training Program Logo
  • The High Road Training Program
  • The High Road Article Series
  • The Friendliest Trucker's Forum Ever!
  • Email Updates When New Articles Are Posted

Apply For Paid CDL Training Through TruckingTruth

Did you know you can fill out one quick form here on TruckingTruth and apply to several companies at once for paid CDL training? Seriously! The application only takes one minute. You will speak with recruiters today. There is no obligation whatsoever. Learn more and apply here:

Apply For Paid CDL Training