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.