CDL Combination Vehicles TestDriving Combination Vehicles SafelyMedium
A commercial driver is operating a combination vehicle on a downhill grade during a rainstorm. The driver notices the rear of the trailer beginning to sway from side to side. What is the most appropriate immediate action to take?
- AIncrease engine RPM and downshift to pull the trailer straight.
- BRelease the accelerator and gently apply the service brakes if necessary, without locking them.
- CMake small, quick steering corrections in the direction of the sway.
- DApply the trailer hand brake firmly to stop the sway.
Show answer & explanationAnswer & explanation
Correct answer: B. Release the accelerator and gently apply the service brakes if necessary, without locking them.
Trailer sway, or 'fishtailing,' can be dangerous. Releasing the accelerator shifts weight to the drive wheels, increasing traction, and gentle application of service brakes can help to straighten the vehicle without causing a jackknife, especially on a wet downgrade.
Why the other options are wrong
- A. Increasing engine RPM and downshifting might exert more force on the trailer, potentially worsening the sway.
- C. Small, quick steering corrections can be counterproductive and make the sway worse or lead to overcorrection.
- D. Applying the trailer hand brake firmly can lock the trailer wheels, causing a jackknife, especially on a wet surface.
Trailer Sway Correction
When a trailer sways, the driver should release the accelerator and apply gentle, controlled braking to regain stability.
- Avoid hard braking or trailer hand brake.
- Gentle accelerator release helps.
- Smooth steering inputs are key.
Memory trick: Swaying trailer's plight, ease the gas, brake light.