CLP - Commercial Learner's Permit Combination Vehicle Operations Questions and Answers 1 — Questions and Answers
Question 1: When driving a combination vehicle, the 'crack-the-whip' effect is a significant danger. Which of the following is most likely to cause the rear trailer to roll over?
- Driving slowly around a wide, sweeping curve.
- Making a sudden or quick lane change. (Correct answer)
- Applying the trailer hand brake firmly while turning.
- Accelerating smoothly on a straight highway.
Correct answer: Making a sudden or quick lane change.
The 'crack-the-whip' effect, also known as rearward amplification, happens when a driver makes a quick steering movement, like a sudden lane change. This causes the rear-most trailer to swing out with greater force, which can lead to a rollover, even if the tractor remains stable.
Question 2: You are coupling a tractor to a semitrailer. Before you back under the trailer, the trailer is at the correct height when:
- The landing gear is fully retracted and off the ground.
- The kingpin is about two inches lower than the fifth wheel.
- The trailer will be raised slightly when the tractor backs under it. (Correct answer)
- The fifth wheel makes firm contact with the trailer apron without lifting it.
Correct answer: The trailer will be raised slightly when the tractor backs under it.
The trailer should be just low enough that the tractor's fifth wheel will slide under and lift the front of the trailer slightly. If the trailer is too low, the tractor may strike the kingpin incorrectly. If it is too high, it may not couple correctly and could damage the landing gear or fifth wheel.
Question 3: A driver is operating a tractor without a trailer attached, a practice known as 'bobtailing'. Compared to a fully loaded tractor-trailer, how does a bobtail tractor's stopping distance change?
- It is significantly shorter due to the reduced weight.
- It is about the same, as the brakes are designed for the tractor.
- It can be longer because there is less weight on the drive axles for traction. (Correct answer)
- It depends entirely on the road surface condition.
Correct answer: It can be longer because there is less weight on the drive axles for traction.
It is a common misconception that a lighter bobtail tractor stops faster. In reality, it can take longer to stop than a fully loaded unit. The braking system is designed for a heavy load, and without the trailer's weight providing traction on the rear axles, the wheels can lock up easily, causing a skid and increasing the stopping distance.
Question 4: What is the primary, approved use of the trailer hand valve (also known as the trolley valve or Johnson bar)?
- To prevent the vehicle from rolling back on a hill.
- To test the trailer service brakes. (Correct answer)
- To assist with making tight turns.
- For regular parking instead of the spring brakes.
Correct answer: To test the trailer service brakes.
The trailer hand valve should only be used to test the application of the trailer's service brakes to ensure they are working correctly. It should not be used for parking, as air could leak out, or for braking during driving, as it can cause the trailer wheels to lock up and skid.
Question 5: When a combination vehicle turns a corner, the rear wheels of the last trailer follow a different path than the front wheels of the tractor. This is called:
- Rearward amplification
- Off-tracking (Correct answer)
- Axle drift
- Yaw instability
Correct answer: Off-tracking
Off-tracking, or 'cheating,' is the term used to describe how the rear wheels of a vehicle or combination vehicle follow a path inside the path of the front wheels when turning. The longer the vehicle, the greater the amount of off-tracking.
Question 6: Which of the following statements about inspecting a combination vehicle is TRUE?
- There should be a noticeable gap between the upper and lower fifth wheel after coupling.
- The landing gear should be raised only until it just lifts off the pavement before driving.
- A lack of grease on the fifth wheel plate can cause steering problems. (Correct answer)
- The safety latch for the fifth wheel jaw should be in the open position for driving.
Correct answer: A lack of grease on the fifth wheel plate can cause steering problems.
The fifth wheel plate must be properly lubricated. If it is not, the friction between the tractor and trailer can create resistance that makes steering difficult and can damage the parts. After coupling, there should be no gap, the landing gear must be fully raised, and the safety latch must be engaged.
CLP - Commercial Learner's Permit Combination Vehicle Operations Questions and Answers 1
When driving a combination vehicle, the 'crack-the-whip' effect is a significant danger.
Which of the following is most likely to cause the rear trailer to roll over?