CDL Combination Vehicles TestDriving Combination Vehicles SafelyEasy
You are driving a combination vehicle on a wet, slippery road. To prevent a jackknife, which of the following actions is most critical?
- AApply the trailer hand brake firmly and continuously.
- BAvoid sudden braking and downshift to a lower gear.
- CSteer sharply in the opposite direction of the trailer's drift.
- DIncrease your speed to maintain momentum.
Show answer & explanationAnswer & explanation
Correct answer: B. Avoid sudden braking and downshift to a lower gear.
Sudden braking on slippery surfaces can lock up the drive wheels, causing the tractor to pivot and the trailer to swing out, leading to a jackknife. Downshifting helps control speed without relying solely on the service brakes, reducing the risk of wheel lock-up.
Why the other options are wrong
- A. Applying the trailer hand brake alone can lock the trailer wheels, causing the trailer to swing out (trailer jackknife) even if the tractor wheels are not locked.
- C. Steering sharply in the opposite direction of a trailer's drift (counter-steering) is a recovery technique for a trailer swing, but doing it sharply can worsen the situation or cause loss of control if the vehicle is already in an unstable state. Preventing the drift in the first place is more critical.
- D. Increasing speed on a slippery road significantly increases the risk of losing control and jackknifing.
Jackknife Prevention
A jackknife occurs when the tractor and trailer fold in on each other, typically due to loss of traction. Prevention focuses on smooth, controlled driving.
- Avoid sudden braking, especially on slippery surfaces.
- Use engine braking (downshifting) to help slow down.
- Maintain a safe following distance.
- Be aware of road conditions and adjust speed accordingly.
Memory trick: Smooth moves keep the truck in a groove.