How Commercial Truck Maintenance Failures Lead to Crashes

A loaded tractor-trailer depends on a few dozen components that wear every mile: brake linings, slack adjusters, air lines, tires, steering linkages, spring hangers, the fifth wheel. When one fails, the driver usually gets little warning and little room to recover. Federal rules treat that risk as the carrier’s problem to manage before the truck leaves the yard, and they require paperwork showing the carrier did.

Brakes come first

When the Large Truck Crash Causation Study coded the conditions present at serious truck crashes from 2001 to 2003, brake problems led every category: 29.4 percent of trucks had a brake failure, an out-of-adjustment brake or a similar defect recorded¹. That figure is an associated factor, a condition present at the crash, not a finding that the brakes caused it. FMCSA’s report warns that no associated factor should, by itself, be read as the cause of a crash¹.

The study’s analysis brief adds weight. Trucks with brake problems were 2.7 times as likely as trucks without them to be assigned the “critical reason”, the immediate failure that made the crash unavoidable². That is a real increase, if smaller than for driver behaviors such as following too closely. Where the truck itself was the vehicle that failed, the report found the failures concentrated in three areas: braking capacity, tire or wheel failure, and cargo shift¹.

The failure modes that matter most

Air brakes and adjustment. Most heavy trucks stop with air-actuated drum or disc brakes. As linings wear, the pushrod in each brake chamber travels farther before the shoes meet the drum, and past a set point the brake delivers less force. One brake out of adjustment may go unnoticed. Several can lengthen stopping distance enough to turn a near miss into a collision. Part 393 sets maximum pushrod stroke limits by chamber type, and vehicles with air brakes built on or after October 20, 1994 must have automatic brake adjusters³. Automatic adjusters reduce the problem without ending it. They can wear out or malfunction, and a brake that keeps going out of adjustment can point to a worn component elsewhere in the brake assembly. Part 396 also requires that anyone responsible for brake inspection, maintenance or repair meet minimum qualifications⁴.

Tires. Part 393 bars operating on a tire with exposed ply or belt material, tread or sidewall separation, a flat or an audible leak. Front tires on a truck or tractor need at least 4/32 inch of tread depth. Other positions need 2/32 inch³. A steer tire failure at highway speed can pull a truck across lanes before the driver reacts.

Steering and suspension. Part 393 covers steering wheel lash, cracked or missing axle positioning parts, and broken or shifted leaf springs³. These failures tend to develop slowly, as handling problems a driver may learn to live with.

Lighting and conspicuity. Lamps and reflective devices must not be obscured by the load, its covering or dirt. Trailers 80 inches or wider with a gross vehicle weight rating over 10,000 pounds, built on or after December 1, 1993, must carry retroreflective sheeting, reflex reflectors or a combination of the two³. A dark or dirty trailer stopped on a shoulder at night is hard to see until a following driver is close.

Coupling devices. The fifth wheel must be securely mounted and must have a locking mechanism that prevents the halves from separating without a deliberate release³. A trailer that separates on the road leaves a loaded box with no tractor.

Cargo securement. Subpart I of Part 393 requires cargo to be contained, immobilized or secured so it does not leak, spill, blow or fall from the vehicle, and does not shift enough to affect the vehicle’s stability or maneuverability. Tiedowns must be rated to withstand set forces, including 0.8 g of forward deceleration and 0.5 g laterally³. In the LTCCS, cargo shift was coded for only 4 percent of trucks. When it was coded, it carried a relative risk of 56.3, the highest in the study¹².

What Part 396 requires

Part 396 sets out a chain of inspections, each with its own record and its own retention period⁴.

Systematic maintenance. Under 396.3, every motor carrier must “systematically inspect, repair, and maintain” every vehicle under its control, and parts must be in safe and proper operating condition at all times. Records must identify the vehicle, show the nature and due date of scheduled work, and record what was done and when⁴. The rule sets no mileage or calendar interval. The carrier sets the schedule and has to follow it.

The daily report. At the end of each day’s work, the driver must report in writing on each vehicle driven, covering at least service and parking brakes, steering, lights and reflectors, tires, horn, wipers, mirrors, coupling devices, wheels and rims, and emergency equipment. A report is required only if a defect is found or reported. Before the vehicle runs again, the carrier must repair any listed defect likely to affect safety and certify the repair, or certify that none was needed⁴.

Before the next trip. Under 396.13, the driver must be satisfied the vehicle is safe to operate, review the last inspection report, and sign it to acknowledge any required repairs were certified⁴.

The annual inspection. Every commercial motor vehicle, including each trailer in a combination, must pass a periodic inspection of the components in Appendix A to Part 396 at least once every 12 months, performed by a qualified inspector, with documentation on the vehicle⁴.

Above all of these sits 396.7: a vehicle may not be operated in a condition likely to cause a crash or breakdown⁴.

Roadside inspections and out-of-service orders

State and federal inspectors also stop trucks at scales and roadside sites, using the Commercial Vehicle Safety Alliance’s inspection procedures. A Level I inspection is the full check of driver credentials and the vehicle’s mechanical condition. Level II is a walk-around limited to what can be checked without going under the vehicle. Level V is a vehicle-only inspection⁶.

The pass-fail standard is CVSA’s North American Standard Out-of-Service Criteria, updated each year effective April 1⁵. A vehicle with an out-of-service condition cannot be operated until the defect is repaired. When FMCSA inspectors place a vehicle out of service, federal rules bar anyone from operating it or removing the out-of-service sticker until the required repairs are done, though it may be towed away by crane or hoist. The carrier must certify within 15 days that the violations were corrected⁴.

The results show where trucks fail. During CVSA’s 2026 International Roadcheck, inspectors across North America placed 10,350 vehicles out of service, 19 percent of the vehicles inspected. Brake systems were the top vehicle out-of-service violation at 3,379, or 24.3 percent of all vehicle out-of-service violations. Tires followed at 20.9 percent. A separate brake category, vehicles with 20 percent or more of their brakes defective, made up another 14.9 percent. Cargo securement came to 12.4 percent and lights to 11.9 percent⁷. CVSA says brake-related violations “continue to be one of the leading reasons vehicles are placed out of service”⁸.

Why the records matter after a crash

A defect found at roadside is a violation. A defect found after a crash raises a different question: did the carrier know, or should it have known?

The maintenance file is where that question gets answered. Investigators and litigants look for:

• Daily reports listing a defect, and whether the repair was certified before the next trip.
• Repeated write-ups of the same component, which can suggest a problem was patched rather than fixed.
• Gaps between the carrier’s own schedule and the work actually done.
• Annual inspection reports, and whether the inspector was qualified.
• Prior roadside inspections and out-of-service orders on the same vehicle.
• Who worked on the brakes, and whether that person met the brake inspector qualifications.

Retention periods are short. Daily inspection reports need be kept only 3 months⁴, which is why preservation requests often go out soon after a serious crash. A post-crash inspection of the truck itself, measuring pushrod stroke, lining thickness and tire condition, can confirm or contradict the paperwork. Our guide to evidence after a truck crash covers the full set of records, and our explainer on liability in commercial vehicle collisions covers how maintenance failures can bear on a carrier’s responsibility, which varies by state and by the facts. For how vehicle failures rank against driver and roadway factors, see our analysis of the leading causes of large truck crashes.