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A jackknife truck accident occurs when a tractor-trailer brakes too hard on a slippery road. This can happen in one of two ways. When the trailer wheels lock up, the trailer wants to continue sliding down the road past the tractor. This causes the back of the trailer to fishtail about the trailer hitch. Meanwhile, the tractor is braking without skidding. If the truck driver fails to recover from this, the back of the trailer will continue to fishtail forward while pivoting on the hitch until it forms the classic.