What is a 'high hitch' and why is it dangerous?

A high hitch (or 'high coupling') occurs when the kingpin sits on top of the closed fifth wheel jaws rather than being captured inside them. It happens when the fifth wheel height is wrong relative to the trailer apron during coupling, often because the trailer was set too high on its landing gear. The trailer appears to be connected, the locking arm may even latch behind the kingpin, but the kingpin is not actually engaged in the throat of the jaws. The trailer can separate from the tractor at any moment, including immediately upon driving away. The tug test (pulling forward against the locked kingpin) is the primary defense — a high-hitched trailer will not pass the tug test. Always perform the tug test, then visually inspect the engagement from underneath with a flashlight.