Jacknife Brake Accident

Jackknifing means the accidental folding of an articulated vehicle (i.e. one towing a trailer) such that it resembles the acute angle of a folding pocket knife. If a vehicle towing a trailer skids, the trailer can push it from behind until it spins round and faces backwards. This may be caused by equipment failure, improper braking, or adverse road conditions such as an icy road surface.

In analysis of jackknife accidents, it was found that in an improperly set brake system the trailer axles are locked sooner than the tractor axles under heavy braking. Jackknife could occur even when the lateral acceleration is at extremely low levels. Rollover and jackknifing accidents are responsible for a significant percentage of the accidents and casualties of commercial vehicles.

Brake imbalance is another common cause for loosing control of the air-braked trucks causing an accident. If a truck does not have good brake balance, it will have a tendency toward either jackknifing or trailer swing-out. Jackknifing occurs when the tractor's drive axles achieve a higher level of braking force than the trailer axles. When this happens in an emergency or low traction situation, the tractor drive axles will likely lock up while the trailer axles are still rolling. With the tractor's drive axles locked, they will lose directional stability and the un-braked trailer load will push the tractor into a rotation around the king pin. Trailer swing-out is similar to a jackknife, but occurs when the trailer axles achieve a higher level of braking force than the tractor. With the trailer brakes locked and directional stability lost, the tractor will drag the trailer, which will then begin to swing out.

There are three brakes in an 18-wheeler tractor-trailer truck:

• The steering axle brakes
• The drive axle brakes, and
• The trailer axle brakes.

When the steering axle brakes lock up, the driver cannot steer and the truck will move straight ahead regardless of the wheel angle. When a tractor trailer's drive axle brakes lock up, jackknifing will occur. When the trailer axle brakes lock up, you will get trailer swing-out, affecting the directional stability of the truck.

The basic problem is that pneumatic tires only offer certain traction and if that is completely used in braking, there is nothing left to resist even a small lateral force. If you can keep the axles from locking up, even 5% short of lock up, you can generally preserve directional stability and even some steering capability. But this can be hard to do without ABS (anti-lock brake system), especially with unbalanced brakes or a poorly distributed load. Thus ABS can prevent jackknifing.. However, many trucks are missing ABS for one, or more of these braking systems.

If you are involved in tractor trailer accident due to brakes locking up, such as a jackknife, contact us for a free consultation to discuss your case with an expert.