Free 20-question practice test on tractor-trailer coupling, uncoupling, air line connections, and the handling characteristics that make combination vehicles different from any other vehicle on the road.
All Alabama CDL Practice Tests by Chapter
Off-tracking is when the rear wheels follow a shorter arc than the front wheels during a turn. The longer the vehicle, the greater the off-tracking. This is why combination vehicle drivers must make wide turns to prevent rear wheels from riding over curbs or pedestrians.
After coupling, apply the trailer brakes, then gently try to pull the tractor forward. The trailer should not move. Then visually confirm the fifth wheel jaws are locked around the kingpin by looking under the front of the trailer.
You need a Class A CDL to operate any combination vehicle with a gross combination weight rating (GCWR) of 26,001 lbs or more, provided the trailer has a GVWR over 10,000 lbs. This covers standard tractor-trailers.
Connect the emergency (red) line first, then the service (blue) line. Also ensure the electrical cord is connected. Never move the vehicle before verifying both glad hands are fully locked and air flows to the trailer.
Jackknifing occurs when drive wheels lock up during hard braking, causing the rear of the trailer to swing toward the cab. Smooth, controlled braking prevents lockup. Anti-lock brake systems (ABS) help prevent jackknifing by preventing wheel lockup.