CDL General Knowledge TestCombination Vehicles (if applicable)Hard
A driver needs to perform a 'tug test' after coupling a tractor to a semi-trailer. What is the correct procedure for this test?
- AApply both tractor and trailer parking brakes, then attempt to pull forward.
- BApply the tractor parking brakes, release trailer parking brakes, and gently pull forward.
- CRelease both tractor and trailer parking brakes, then gently pull forward.
- DApply trailer parking brakes, release tractor parking brakes, and gently pull forward.
Show answer & explanationAnswer & explanation
Correct answer: D. Apply trailer parking brakes, release tractor parking brakes, and gently pull forward.
The tug test verifies that the fifth wheel locking jaws are securely engaged with the kingpin. By applying the trailer brakes and releasing the tractor brakes, a gentle pull forward will confirm the connection is solid and the trailer won't separate.
Why the other options are wrong
- A. Applying both brakes would prevent any movement and thus any test of the coupling's strength.
- B. Releasing trailer brakes would allow the trailer to roll, defeating the purpose of the tug test.
- C. Releasing both brakes would allow the entire combination to move freely, not testing the coupling.
Tug Test (Coupling)
A procedure performed after coupling to verify that the fifth wheel locking jaws are securely engaged with the kingpin.
- Trailer parking brakes applied, tractor parking brakes released.
- Tractor gently pulled forward.
- Confirms secure connection, prevents separation.
Memory trick: Trailer holds, tractor tugs, connection bugs.