What Is Split Coupling on commercial trailers?

faqs -> product-knowledge

Split coupling is the frowned-upon practice of reversing the tractor fifth wheel under the trailer bed plate just enough to support the trailer but not enough to couple positively with the trailer kingpin. This provides the driver with more room between the tractor cab and the trailer front bulkhead in order to couple up the "Suzie" lines with greater ease. Once all lines have been connected, the driver then continues reversing the tractor until the fifth wheel clamps onto the kingpin.

This practice significantly increases the risk of trailer rollaway.  If a trailer has been "dropped" without applying the park brake, when the red line is re-connected, the trailer is free to roll away.