What does "Jackknife" refer to in vehicle operation?

The term "Jackknife" in vehicle operation specifically refers to a situation where a trailer pivots at a sharp angle to the cab, creating a configuration that resembles the folding of a pocket knife. This usually occurs when the trailer wheels lose traction, causing it to swing out to the side. The angle created can make the vehicle difficult to control and poses a significant safety hazard, as it can lead to a total loss of control, potentially resulting in a collision or accident. Understanding this term is critical for drivers, especially those operating heavy vehicles, as it highlights the importance of maintaining control during turns and emergency maneuvers.