Combination Vehicles
Combination Vehicles
The Combination Vehicles test covers tractor-trailers and other combinations: coupling and uncoupling, fifth wheel and kingpin checks, air-line connections, trailer brake tests, turning, off-tracking, and emergency control.
Core rules
- Before coupling, check the trailer height, chock the wheels, and inspect the fifth wheel. Back under slowly, listen for the lock, and perform a tug test with the trailer brakes applied. Then visually confirm the jaws are closed around the kingpin and the safety latch is engaged.
- Connect the service (blue) and emergency (red) air lines to the correct glad hands; crossed lines can release trailer brakes or prevent them from applying. After connecting, charge the trailer and test that the trailer brakes apply and release.
- Raise the landing gear fully and secure the crank handle. Check that the trailer apron is not resting on the tractor frame.
- A combination turns around a pivot point at the rear of the tractor. The trailer off-tracks-cuts the corner-so swing wide before the turn, not during it. The last trailer in a multi-trailer combination has the greatest rearward amplification.
Worked example
A driver backs under a 53-foot trailer, hears the fifth wheel lock, and pulls forward without a tug test. At 55 mph the trailer separates. The missed step: after locking, the driver should apply the trailer brakes, pull gently against them, and watch for movement. If the tractor moves and the trailer does not, the coupling is holding. A visual check of the jaws and safety latch confirms it. The tug test is not a substitute for the visual check, and the visual check is not a substitute for the tug test.
Traps
Do not assume a loud click means safe coupling. Do not cross the air lines or leave the trailer emergency line disconnected. Do not turn tightly before the trailer clears the curb. In Kansas crosswinds, an empty trailer is especially prone to sway, so reduce speed and avoid sudden steering.