CDL General Knowledge TestCombination Vehicles (if applicable)Medium
To prevent a 'jackknife' when braking a combination vehicle, especially on slippery surfaces, what is the most effective technique?
- AShift into a lower gear and use engine braking only.
- BApply the trailer hand valve firmly and continuously.
- CApply the brakes gradually and lightly, maintaining steering control.
- DBrake hard and apply steady pressure until the vehicle stops.
Show answer & explanationAnswer & explanation
Correct answer: C. Apply the brakes gradually and lightly, maintaining steering control.
Gradual and light braking, combined with maintaining steering control, is crucial to prevent jackknifing. Hard braking, especially with the tractor, can lock the drive wheels and cause the tractor to pivot, leading to a jackknife. Using the trailer hand valve alone can lock trailer wheels, also causing a jackknife.
Why the other options are wrong
- A. While engine braking is useful, relying on it solely might not provide sufficient stopping power in an emergency and can still lead to loss of control if too aggressive.
- B. Applying the trailer hand valve can easily lock the trailer wheels, causing a trailer jackknife.
- D. Hard braking on slippery surfaces is a primary cause of jackknifing, as it can lock wheels and lose traction.
Jackknife Prevention (Braking)
Strategies used to avoid a jackknife (where the tractor and trailer fold together) when braking a combination vehicle, particularly on low-traction surfaces.
- Avoid locking wheels.
- Use gradual, controlled braking.
- Maintain steering control.
Memory trick: Smooth and slow, then you can go.