CDL Doubles and Triples Practice Test 3 — Questions and Answers
Question 1: When making a quick lane change with doubles, what is the main danger?
- The rear trailer can roll over or swing into another lane (Correct answer)
- The headlights dim
- The tractor loses fuel pressure
- The horn fails
Correct answer: The rear trailer can roll over or swing into another lane
Sudden steering amplifies sway in the rear trailer, risking rollover or a lane intrusion.
Question 2: Why should you inspect the air lines on a converter dolly carefully?
- Air leaks or crossed lines can cause brake failure (Correct answer)
- They control the headlights
- They power the cab heater
- They adjust the mirrors
Correct answer: Air leaks or crossed lines can cause brake failure
Damaged or improperly connected air lines can prevent the dolly and rear trailer brakes from working.
Question 3: How can you check that the second trailer's kingpin is locked into the dolly's fifth wheel?
- Pull gently against the pin with the dolly secured and inspect the locking jaws (Correct answer)
- Tap the trailer wall
- Watch the dashboard light only
- Listen for the engine RPM
Correct answer: Pull gently against the pin with the dolly secured and inspect the locking jaws
A gentle pull test plus visual inspection of the locking jaws confirms a secure kingpin coupling.
Question 4: What is the correct order when coupling doubles to keep trailers from rolling?
- Secure the second trailer brakes before backing the dolly under it (Correct answer)
- Release all brakes before coupling
- Couple while the trailer rolls freely
- Lower the landing gear last
Correct answer: Secure the second trailer brakes before backing the dolly under it
Setting the second trailer's brakes prevents it from rolling while you position the dolly under it.
Question 5: Which axles are most likely to lock up first on an empty doubles combination during hard braking?
- The lightly loaded trailer axles (Correct answer)
- The tractor drive axles only
- None lock up when empty
- The steering axle only
Correct answer: The lightly loaded trailer axles
Lightly loaded or empty trailer axles have less traction and can lock up sooner during hard braking.
Question 6: When you must stop quickly with doubles, what braking method is recommended for vehicles without ABS?
- Controlled or stab braking to keep the vehicle straight (Correct answer)
- Slam and hold the brakes fully
- Pump the throttle
- Use the trailer hand valve alone
Correct answer: Controlled or stab braking to keep the vehicle straight
Controlled or stab braking helps maintain steering and prevents jackknifing in non-ABS combinations.
Question 7: Why should you avoid using only the trailer hand valve to slow doubles and triples?
- It can cause the trailers to skid or jackknife (Correct answer)
- It turns off the headlights
- It overheats the engine
- It deflates the tires
Correct answer: It can cause the trailers to skid or jackknife
Applying only the trailer brakes can make the trailers skid and lead to a jackknife.
CDL Doubles and Triples Practice Test 3
When making a quick lane change with doubles, what is the main danger?