CDL General Knowledge TestCombination Vehicles (if applicable)Medium
When driving a combination vehicle, what is the most effective way to prevent a trailer from 'jackknifing' during hard braking on a slippery surface?
- AApply the trailer hand valve firmly and continuously.
- BApply the foot brake fully and immediately to engage ABS.
- CRelease the foot brake and steer into the skid.
- DLightly apply the foot brake and gradually increase pressure.
Show answer & explanationAnswer & explanation
Correct answer: C. Release the foot brake and steer into the skid.
To prevent a jackknife or recover from one, releasing the foot brake allows the wheels to roll again, regaining steering control. Steering into the skid helps to align the vehicle.
Why the other options are wrong
- A. Applying the trailer hand valve alone can cause the trailer wheels to lock up, initiating or worsening a jackknife.
- B. Applying the foot brake fully can lock up the drive wheels, causing the tractor to skid and potentially jackknife, even with ABS (ABS prevents wheel lock, but can't overcome all traction issues).
- D. Lightly applying the foot brake might not be enough to prevent a jackknife on a slippery surface if the trailer is already starting to skid.
Jackknife Prevention (Braking)
Techniques to avoid or recover from a jackknife during braking, especially on slippery surfaces.
- Avoid locking drive or trailer wheels.
- Release brakes to regain steering.
- Steer into the skid (if safe).
Memory trick: Release the brake, then steer, banish all your jackknife fear.