What Causes a Truck to Jackknife?

What Actually Happens in a Jackknife

A jackknife occurs when the trailer of a semi-truck swings out of alignment with the cab, often at a sharp angle, typically triggered by sudden braking, loss of traction, or a sudden steering correction. The name comes from the folded shape the truck and trailer form, resembling a folding knife, and once it starts, the driver often has very limited ability to correct it.

Because a jackknifing truck can span multiple lanes almost instantly, the accident is rarely limited to a single vehicle, this is one of the more dangerous categories of truck accidents specifically because of how quickly it can escalate into a multi-vehicle event.

Common Causes Investigators Look At

Excessive speed for road or weather conditions, improper braking technique, poorly maintained or malfunctioning brakes, an unevenly loaded trailer, and slick or wet roads are all common contributing factors investigated after a jackknife accident. Often more than one factor is present, for example, a driver braking too hard specifically because they were traveling too fast for the conditions.

Brake imbalance between the tractor and trailer is a particularly common mechanical cause, if the trailer’s brakes engage more aggressively than the cab’s, the trailer can begin to swing even under otherwise normal braking, pointing toward a maintenance failure rather than driver error.

Why These Accidents Cause Such Severe Damage

A jackknifed trailer can block multiple lanes of traffic, creating secondary collisions as other vehicles are unable to stop or avoid the obstruction, often resulting in multi-vehicle accidents with severe injuries. On a highway with fast-moving traffic, the sudden appearance of a jackknifed trailer leaves following drivers very little time to react.

This is why jackknife accidents so often involve multiple, sometimes entirely separate, personal injury claims, drivers who were nowhere near the original cause of the jackknife can still be seriously injured in the resulting chain reaction.

What Evidence Matters

Black box and ELD data, the truck’s maintenance records, weather and road conditions at the time, and witness accounts all help establish what specifically caused the jackknife and who bears responsibility. Maintenance records are particularly important when brake-related mechanical failure is suspected, since they can reveal whether a known issue was ignored.

Post-accident inspection of the truck itself, brakes, tires, and trailer coupling, often needs to happen quickly, before the vehicle is repaired or the evidence is otherwise altered.

Multiple Potentially Liable Parties

As with other truck accidents, a jackknife can trace back to the driver’s choices, the trucking company’s maintenance practices, a third-party maintenance contractor, or even a defective brake component from a manufacturer. Establishing the actual mechanical or human cause is what determines which of these parties bears responsibility.

If You Were Hit by Another Vehicle After a Jackknife

If you were involved in a secondary collision caused by a jackknifed truck blocking the road, rather than the jackknifing truck itself, you may still have a claim against the truck driver or company whose negligence created the hazard that led to your accident. The chain of causation, not just direct contact with the truck, is what matters legally.

Steps After a Jackknife Accident

1. Get medical attention and document all injuries, even if you were in a secondary collision.
2. Photograph the scene, including the truck’s final position and any visible mechanical issues like tire condition.
3. Request the police accident report, which often includes an initial assessment of contributing factors.
4. Send an evidence preservation demand covering the truck’s maintenance history and ELD data.
5. Consult an attorney promptly, given how quickly mechanical evidence can be lost once the truck is repaired or removed.