What a jackknife is, and why it often points to driver or equipment error
A jackknife happens when the wheels of the tractor, usually the drive axles, lose grip and the trailer's momentum pushes it forward and sideways around the coupling. The rig folds like a pocket knife, which is where the name comes from. Once the angle opens up, the driver cannot steer the trailer back into line, and anything in the adjacent lanes is in its path.
A jackknife rarely comes out of nowhere. Something usually breaks the tires' grip: braking too hard, braking in a curve, driving too fast for wet or icy pavement, an empty or lightly loaded trailer, a shifting load, or brakes that are out of adjustment on one axle and grab unevenly. Each of those causes traces back to a decision by the driver, the carrier or whoever loaded or maintained the equipment.
Safety rules that often come up in jackknife cases
Federal rules speak directly to the conditions that cause jackknifes. When snow, ice, sleet, fog, rain or similar conditions affect visibility or traction, a commercial driver must use extreme caution and reduce speed, and must stop driving if conditions become dangerous enough (49 CFR § 392.14). A driver who kept highway speed on a slick Blue Route grade has a hard time squaring that with the rule.
All brakes on the vehicle must be capable of operating at all times (49 CFR § 393.48). Antilock brakes, which help keep wheels from locking under hard braking, are required on truck tractors built on or after March 1, 1997 and on air-braked trailers built on or after March 1, 1998, and the tractor must be able to warn the driver of an ABS malfunction (49 CFR § 393.55). An ABS warning lamp that had been lit for weeks is a maintenance question for the carrier.
Cargo must be secured so that it does not shift enough to affect the vehicle's stability or handling (49 CFR § 393.100(c)). A load that slid forward or to one side in a hard stop can start or worsen a jackknife.
Where jackknifes happen around Upper Darby and Philadelphia
Jackknifes are a highway problem. On I-476, the grades and curves between the Schuylkill Expressway and I-95 punish a driver who brakes late. On the Schuylkill Expressway, short merges and sudden stops in heavy traffic force hard braking. On I-95 through Delaware County and South Philadelphia, a jackknifed trailer can block several lanes and trigger a chain of secondary crashes.
Chain collisions raise hard fault questions. You may have been hit by the trailer itself, by a car that could not stop for the trailer, or both. Sorting out who caused what takes the police report, witness statements, video from traffic cameras or nearby businesses, and the truck's own data.
The evidence that shows why the truck jackknifed
The truck's engine control module can record speed, throttle and brake application in the seconds before a hard-braking event. The electronic logging device shows how long the driver had been on duty. Maintenance and inspection records show the condition of the brakes and ABS. The bill of lading and loading records show what the trailer carried and how heavy it was.
A written preservation demand should reach the carrier quickly, and the tractor and trailer should be inspected before they are repaired or returned to service. Our page on truck black box evidence explains what each of these records contains and how long carriers are required to keep them.
Who can be responsible for a jackknife
The driver is responsible for speed, following distance and braking. The motor carrier is responsible for its driver's conduct on the job and for its own maintenance, training and scheduling decisions; a dispatch schedule that could only be met by driving fast in bad weather is part of the story. A shipper or loader can share fault for an unbalanced or unsecured load, and a repair shop for a brake job done wrong.
Pennsylvania uses modified comparative negligence (42 Pa.C.S. § 7102), so the trucking insurer may argue that you were following too closely or driving too fast yourself. A clear reconstruction of the sequence protects you against that argument.
Next steps and deadlines
Get medical care, keep every record, and write down what you saw: where the trailer ended up, which lanes it blocked, and the weather and road surface. A Pennsylvania injury suit generally must be filed within 2 years (42 Pa.C.S. § 5524), and exceptions exist, but truck evidence can disappear long before that.
Warren I. Siegel, Esq. takes jackknife claims on a 100% contingency fee. There is no attorney fee unless we recover, the firm advances all case costs, and they are repaid only from a recovery. Call (267) 412-4601 or send the free case review form.
Questions People Ask About Jackknife Accident Claims
What is a jackknife accident?
It is a crash in which the trailer of an articulated truck swings out until it forms a sharp angle with the tractor, often sliding across several lanes. Other vehicles are struck by the trailer or collide while trying to avoid it.
Why is it called jackknifing?
Because the tractor and trailer fold toward each other at the hitch, the way the blade of a folding jackknife closes toward its handle.
What usually causes a trailer to jackknife?
The usual trigger is a loss of traction at the tractor's wheels, often from hard or late braking, braking in a curve, speed too high for wet or icy roads, a light or empty trailer, a shifting load, or brakes that are unevenly adjusted. Each of these can point to a driver, carrier, loader or maintenance failure.
How can truck drivers avoid jackknifing?
By slowing down for curves, ramps and bad weather, leaving enough following distance to brake gradually, keeping brakes and antilock systems in working order, and making sure the load is balanced and secured. Federal rules require drivers to reduce speed when conditions affect traction, and to stop driving if conditions become too dangerous. When a driver skips these steps, that failure is evidence of negligence.
Can I recover if I hit the jackknifed trailer myself?
Often, yes. A trailer that suddenly blocks the highway can leave no time to stop. Your own speed and following distance will be examined, but under Pennsylvania's comparative negligence rule a share of fault on your part reduces your recovery rather than ending it, unless your share is greater than the defendants' combined.
Sources
Written for general information by the office of Warren I. Siegel, Esq., Pennsylvania Attorney ID 65342. Last reviewed 2026-09-25. This is not legal advice for your situation, and deadlines vary by claim. Talk to a lawyer before relying on any date.