Underride and Jackknife Crashes: Causes and Evidence
Underride and jackknife crashes are two tractor-trailer crash types that often cause severe injuries. An underride crash happens when a smaller vehicle slides partly or completely beneath a trailer or truck body. In a jackknife, the tractor and trailer fold toward each other, often across several lanes. Each one raises distinct evidence questions for a truck accident attorney.
Why underride crashes are so dangerous
According to the Insurance Institute for Highway Safety (IIHS), large trucks are taller and have greater ground clearance than cars, which means a lower vehicle can slide beneath a trailer, and strong underride guards can stop that from happening. If a car goes under a trailer, the trailer can intrude into the passenger compartment, bypassing much of the crash protection built into the front of the car.
Rear impact guards on trailers are governed by Federal Motor Vehicle Safety Standards No. 223 and No. 224, found at 49 CFR 571.223 and 571.224, and 49 CFR 393.86 covers rear impact guards on trucks in service. IIHS reports that NHTSA finalized an upgraded rear guard standard in 2022. In a June 2024 report to Congress under the Bipartisan Infrastructure Law, NHTSA estimated an average of 89 deaths a year among light passenger vehicle occupants in two-vehicle crashes in which the passenger vehicle strikes the side of a trailer or semi-trailer and goes under it. A truck accident lawyer will look at whether the trailer had a compliant guard and whether it was damaged before the crash.
What causes a jackknife
A jackknife usually starts with a loss of traction. Commercial driver manuals explain that when trailer wheels lock, the trailer tends to swing around, and that this is more likely when the trailer is empty or lightly loaded. Hard braking, speed too fast for conditions, wet or icy pavement, out-of-adjustment brakes and shifting cargo can all contribute. Federal Motor Vehicle Safety Standard No. 121 covers air brake systems, including antilock brakes, but antilock brakes reduce wheel lockup without eliminating every skid.
Photos https://truckaccidentlawyers.wiki/geography/united-states/georgia/metro-atlanta/smyrna/ of the folded rig show where the vehicles came to rest, not which unit lost control first. A tractor skid and a trailer swing can look alike after the fact, so reconstruction depends on tire marks, ECM speed and brake data, brake adjustment readings and the load records. A semi-truck crash lawyer will usually ask for the brake inspection history and the bill of lading for that reason.
Rollovers and secondary crashes
FMCSA's Large Truck and Bus Crash Facts 2022 states that overturn, or rollover, was the first harmful event in 4 percent of fatal crashes involving large trucks. A jackknifed or overturned trailer can block multiple lanes, leading to secondary collisions with vehicles that cannot stop in time. Poor trailer visibility at night is another recurring issue in underride cases, so investigators check the retroreflective sheeting required on many trailers under 49 CFR 393.11. A truck wreck attorney may review the police crash report and scene photos for lighting and visibility problems.
Liability and evidence in these crashes
Responsibility can extend beyond the driver: the trucking company for maintenance and training, the loader for cargo securement under 49 CFR Part 393, and the manufacturer if a guard or brake component was defective. A big rig accident attorney usually asks that the trailer, the guard and the brake parts be kept before any repairs. Each state has its own statute of limitations and fault rules, and this is general information, not legal advice or a prediction about any claim.