Jackknifing

Jackknifingis the folding of anarticulated vehicleso that it resembles the acute angle of a foldingpocket knife.If a vehicle towing a trailer skids, the trailer can push the towing vehicle from behind until it spins the vehicle around and faces backwards. This may be caused by equipment failure, improper braking, or adverse road conditions such as an icy road surface. In extreme circumstances, a driver may attempt to jackknife the vehicle deliberately to halt it following brake failure.

Trailer swing[edit]

When a trailer skids to one side, this is known as atrailer swingortrailer slew.This can occur on a slippery road surface, often where there is acant.This is not the same as jackknifing and is not as serious, as the trailer will move back into line as the vehicle continues forwards. The driver must be aware, however, that the trailer could slide up against parked cars or aguard rail,or that the wheels could slide into a ditch. This situation can occur especially when the trailer is empty or lightly loaded, and weather conditions cause violent gusts ofcrosswind.^{[citation needed]}

Anti-jackknife devices[edit]

One system with limited success was a device that mechanically limited the angle which a trailer could swing.
A much more successful system was to fit the tractor withanti-lock brakes.Fitted originally to airplanes in the 1950s, anti-lock brakes have significantly reduced the number of heavy-vehicle accidents.
Electronic brakeforce distributionvaries the pressure to the rear brakes during heavy load or hard braking, enhancing driver control.^[1]
Tractorswere once commonly fitted with a lever in the cab to operate the trailer brakes (a trolley brake). The vehicle could be slowed or stopped using the trailer brakes only. Theoretically, this was a guaranteed way to prevent jackknifing; however, frequent use of the trailer brakes alone caused them to overheat andfadewhile the tractor brakes remained fresh. In the event of anemergency stop,the driver, applying the foot brake, could cause the trailer to jackknife because the tractor brakes lock while the trailer brakes are ineffective due to previous overheating. Trolley brakes largely disappeared from tractor units in North America in the 1980s and 1990s
An alternative to having a trailer brake lever in the cab is to fit the trailer with anelectromagnetic brake.

References[edit]

^Brake Pressure Regulator – Patent 3762776

[1] Brake Pressure Regulator – Patent 3762776

[1]

v t e Traffic collisions
Main topics	Epidemiology Hit and run Park-to-reverse Roadside memorial Rollover Vehicle extrication Vehicle recovery Traffic collision reconstruction
Road collisions	Back-up collision Deer–vehicle collisions Head-on collision Jackknifing Multiple-vehicle collision Rear-end collision Run-off-road collision Side collision Single-vehicle crash
Causes	Assured clear distance ahead Distracted driving Driving under the influence Road rage
Lists of traffic collisions	Before 2000 2000–present By death toll
Related lists	List of bridge failures List of level crossing crashes List of people who died in traffic collisions
Template:Automotive handling Template:Traffic law

Trailer swing[edit]

Anti-jackknife devices[edit]

See also[edit]

References[edit]