CDL Combination Vehicles Practice Test 1 — Questions and Answers
Question 1: A fully loaded rig is _________ times more likely to roll over in a crash than an empty rig.
- 5
- 10 (Correct answer)
- 15
- 20
Correct answer: 10
A fully loaded rig has a significantly higher center of gravity and much greater momentum compared to an empty one. This increased mass and higher center of gravity make it far more susceptible to rolling over during sudden maneuvers or impacts. Therefore, the risk of a rollover crash is drastically amplified when the vehicle is fully loaded.
Question 2: When following behind other vehicles, you should follow
- At least one second for every 20 feet of your vehicle length
- At least two seconds for every 10 feet of your vehicle length
- At least two seconds for every 10 feet of your vehicle length, plus one second if going over 50 MPH
- At least one second for every 10 feet of your vehicle length, plus one second if going over 40 MPH (Correct answer)
Correct answer: At least one second for every 10 feet of your vehicle length, plus one second if going over 40 MPH
The 'one second for every 10 feet of vehicle length' rule provides a basic safe following distance. Adding an extra second when traveling over 40 MPH accounts for the increased stopping distance and reduced reaction time at higher speeds. This adjustment ensures adequate space to react and stop safely, especially with a large commercial vehicle.
Question 3: A trailer jackknife is likely to happen when
- The vehicle has a high center of gravity
- The wheels of the trailer lock up (Correct answer)
- The front drive wheels lose traction
- There is too much weight on the steering axles
Correct answer: The wheels of the trailer lock up
A trailer jackknife occurs when the trailer pushes the tractor from behind, causing the trailer to swing out to the side. This typically happens when the trailer wheels lock up, losing traction and sliding, while the tractor continues to move forward. The locked trailer wheels act as a pivot point, leading to the dangerous jackknife angle.
Question 4: What is the fastest and best way to recognize that your trailer has started to skid?
- Feeling your steering wheel shake
- Listening for the distinctive skidding sound
- Seeing it in your mirrors (Correct answer)
- Feeling your vehicle pull to the side
Correct answer: Seeing it in your mirrors
The fastest and most reliable way to detect a trailer skid is by observing it in your mirrors. You will see the trailer begin to swing out of alignment with the tractor. Relying on feel or sound can be delayed or less distinct, making visual confirmation crucial for timely corrective action.
Question 5: If your trailer begins to skid, you should
- Maintain light pressure on your brakes until the trailer straightens out
- Release your brakes until the trailer wheels grip the road again (Correct answer)
- Turn the steering wheel in the direction of the skid
- Apply to the trailer hand brake to straighten out the trailer
Correct answer: Release your brakes until the trailer wheels grip the road again
If your trailer begins to skid, the most effective action is to release the brakes. This allows the trailer wheels to unlock and regain traction with the road surface. Once traction is restored, the trailer can straighten out, preventing a jackknife or further loss of control.
Question 6: Which of the following will help prevent a rollover:
- Keep the cargo load centered on the rig
- Drive slowly around turns
- Keep the cargo as close to the ground as possible
- All of the above (Correct answer)
Correct answer: All of the above
All these actions contribute to preventing rollovers. Keeping cargo centered and low reduces the vehicle's center of gravity, making it more stable. Driving slowly around turns minimizes centrifugal force, which is a primary cause of rollovers for tall or heavy vehicles. Combining these practices significantly enhances stability.
Question 7: On the trailer air lines of a combination vehicle, the service line connects to the _________ on the trailer to control the pressure to the trailer brakes.
- Glad hands
- Trailer hand valve
- Relay valves (Correct answer)
- Tractor protection valve control
Correct answer: Relay valves
On a combination vehicle, the service line connects to the relay valves on the trailer. These relay valves are crucial because they quickly send air pressure from the trailer's air tanks to the brake chambers, allowing for faster and more effective braking of the trailer. This system ensures synchronized braking between the tractor and trailer.
Question 8: On older trailers, what will happen if the emergency and service air lines are crossed?
- Nothing will happen, they are designed to be interchangeable
- The trailer spring brakes will release
- Water and oil will build up in the air tanks
- You could drive away, but you will not have trailer brakes (Correct answer)
Correct answer: You could drive away, but you will not have trailer brakes
If the emergency and service air lines are crossed on an older trailer, the trailer's emergency (spring) brakes will release, but the service brakes will not function. This means you could drive away, but you would have no way to apply the trailer's service brakes. This is a critical safety hazard as the trailer would not contribute to stopping the rig.
Question 9: When hoses are not in use, why should the trailer gland hands be locked together or attached to dead end or dummy couplers?
- To prevent mix-up of the emergency and service lines
- To keep the air supply clean (Correct answer)
- To keep the air supply regulated
- To prevent a loss of air pressure
Correct answer: To keep the air supply clean
Locking glad hands together or attaching them to dummy couplers when not in use is essential to keep the air supply clean. This prevents dirt, moisture, and other contaminants from entering the air lines and the trailer's air brake system. Contamination can lead to malfunctions, reduced braking efficiency, and costly repairs.
Question 10: If the trailer protection valve malfunctions, which of the following may occur?
- A leak or trailer break away could drain all the air from the brake system (Correct answer)
- Nothing will happen
- The trailer air pressure will increase
- The glad hands may uncouple
Correct answer: A leak or trailer break away could drain all the air from the brake system
The trailer protection valve is designed to prevent a complete loss of air pressure in the tractor's brake system if there's a major leak or breakaway in the trailer. If this valve malfunctions, a leak or a trailer breaking away could indeed drain all the air from the entire brake system, rendering both the tractor and trailer brakes inoperable. This is a critical safety feature.
CDL Combination Vehicles Practice Test 1
A fully loaded rig is _________ times more likely to roll over in a crash than an empty rig.