Jackknifing is a major cause of devastation in a traffic accident involving tractor-trailer trucks. Researchers in Greece have now designed a device to prevent this often lethal action. The team’s sliding kingpin device allows the so-called kingpin junction between the front tractor and the trailer to slide along the rear tractor axle and preclude the jackknifing motion of the trailer relative to the tractor.

Jackknifing, in which instability often associated with an empty, or low-weight trailer being towed on a slippery road, leads to catastrophic articulation of the joint between tractor and trailer. Jackknifing is one of the most significant problems facing truck drivers and a major cause of traffic pile-ups and other multiple-vehicle accidents on major roads.

Engineers and designers have attempted to design technologies to prevent jack-knifing, including independent or speed-dependent angle limiters, independent trailer brakes that are operated before the tractor brakes, and load-sensing brake pressure regulators. Unfortunately, success has been very limited and no system is commonly used.

In current trucks, the tractor and semi-trailer combination are hitched together via a mechanical junction - the kingpin - which is static. The team's sliding kingpin system is servo-driven, as is the "fifth" wheel, and this allows the kingpin to slide in a linear fashion along a direction parallel to the rear axle of the tractor. This allows the mechanism to compensate for inordinate movements of the semi-trailer relative to the tractor, especially during hard braking, to reduce or potentially eliminate the possibility of the adverse trailer swing that would otherwise lead to jackknifing.

As with ABS, the sliding kingpin system only comes into play in an emergency situation and does not otherwise interfere with the handling of the vehicle. The sliding mechanism and the semi-trailer act as a planar but horizontal inverted pendulum, and these movements of the kingpin permit the stabilization of the semi-trailer. Modeling suggests that the system is capable of keeping the articulated vehicle in line and constraining jackknifing to very low limits for a wide range of vehicle loading and road conditions.