A jack-knife occurs when the drive wheels of a semi-tractor lose traction, causing the trailer to push the cab sideways. The vehicle folds at the fifth wheel coupling, resembling a folding pocket knife. This usually happens during hard braking on slick roads or empty trailer operations, often resulting in complete loss of control and blockage of multiple highway lanes.
Heard on the job
The rig managed to jack-knife across all three northbound lanes after hitting a patch of black ice.
Insider tip
Anti-lock braking systems have significantly reduced jack-knife incidents, but empty trailers on wet curves remain highly susceptible.