Skid Control, Jackknifing, and Emergency Maneuvers
What this domain covers
Skid and emergency questions test cause and correction. Most combination skids come from excessive speed, hard braking, or abrupt steering, and a jackknife is a skid that folds the tractor and trailer together.
Core rules
- Drive-wheel skid: rear tractor wheels lock and the trailer may swing. Release the brakes, steer in the direction of the skid, and let the wheels roll.
- Steer-axle skid: the front wheels lose grip and steering feels light. Release brake pressure and straighten the wheel to regain grip.
- Trailer skid: the trailer swings out. Release the brakes and steer in the direction of the skid; do not accelerate.
- Jackknife prevention: brake smoothly, avoid sharp steering at speed, and do not use the trailer hand valve in an emergency.
- In an emergency, brake firmly and steer if ABS is available; do not simply swerve, because a combination can roll over.
Worked example
An empty trailer on wet pavement begins to swing left as you brake for a red light. The correct response is to release the brake, steer left to follow the trailer's direction, and regain control. Holding the brake or steering right would deepen the jackknife.
Traps that cost marks
Locking the brakes; overcorrecting; accelerating to pull out a jackknife; using the trailer hand valve; and swerving at high speed instead of braking. Also, do not assume ABS prevents jackknife-it helps, but speed and steering still matter.