A semitruck jackknifing on the freeway is one of the most hazardous scenarios motorists can encounter while driving. When a truck jackknifes, its driver loses control of both the cab and the trailer of the big rig to the peril of all in close proximity on the road.
What this happens, the cab of the semi moves in one direction while the trailer simultaneously moves in another. Typically, the semitruck winds up in a sort of "V" or "L" shape on the road. Think of the shape of a folding pocket knife in its downward position and you have a good idea of how a jackknifed semi appears.
In colder climates, jackknifing often occurs during snowy or icy conditions. Here in Southern California, those weather conditions are quite rare, but that doesn't mean that jackknifing is as well. Anything that can reduce a large truck's traction on the roads — rain mixed with oil from vehicles, mudslides, the spilled load of another semitruck — can create conditions that increase the risk of jackknife accidents for truckers.
Truck drivers who brake their big rigs improperly can cause them to jackknife if the tires go into a deadly skid on the highway. When the brakes lock up, the semi's trailer swings widely and can wind up completely out of sync with the cab of the truck.
Motorists who spot a swaying trailer on a semitruck would do well to get out of its way. Truckers who see or sense the sway of their trailers can sometimes reduce the risk of jackknifing by letting off the brakes and speeding up.
Full trailers are less likely to jackknife on the freeway. Although it is not possible to always drive with a full load, simply being aware of the heightened risk of jackknifing can reduce the possibility of a devastating highway accident.