Brakes and Tires: The Mechanical Failures Behind the Deadliest Truck Crashes

Ask any roadside inspector, any fleet maintenance director, or any plaintiff's accident reconstructionist what mechanical failure they see behind the worst large-truck crashes, and you'll hear the same two words before they finish the sentence: **brakes and tires.**

It's not a hunch. It's the most consistent finding in commercial-vehicle safety data, and it shows up in two completely independent places: FMCSA's landmark crash-causation research, and the millions of roadside inspections conducted every year. When you put those two data sets next to each other, the picture is hard to argue with — and, importantly for anyone vetting carriers, the same risk is visible in a carrier's public FMCSA record *before* a load ever moves.

Let me walk through what the data actually says, with the caveats it deserves, and then connect it to the screening signals that matter.

What FMCSA's crash-causation research found

The definitive study here is the **Large Truck Crash Causation Study (LTCCS)** — FMCSA and NHTSA's investigation of a nationally representative sample of large-truck crashes that each involved at least one fatality or injury, studied across 2001–2003 at 24 sites in 17 states. It remains the most rigorous look the federal government has taken at *why* big trucks crash.

Two findings stand out:

• Brake problems were coded as an associated factor for nearly 30% of the trucks involved in those crashes — versus only about 5% of the passenger vehicles. Brakes weren't a rounding error; they were present in almost a third of the trucks in serious crashes.
• A truck with brake problems was **roughly 170% more likely** to be coded with the "critical reason" for the crash than a truck without that brake-problem factor. In plain English: brake problems didn't just *coincide* with crashes — they substantially raised the odds that the truck was the thing that caused it.

A careful word on terminology, because it matters and a lot of blogs get it wrong: LTCCS coded "associated factors" and a single "critical reason." An associated factor is something present in the crash, not a definitive sole cause. So the honest statement is not "brakes cause 30% of fatal truck crashes" — it's "**brake problems were the most common vehicle-related factor present in serious truck crashes, and their presence sharply increased crash-causation risk.**" That's a more defensible claim, and it's still damning.

Tires are the other half of the story. The same body of research and NHTSA's tire-related crash work attribute on the order of **5–6% of serious large-truck crashes primarily to tire problems** — blowouts and tread separation chief among them — which works out to roughly 8,000 crashes a year in the study-era estimates. Overall, vehicle/equipment failure of some kind was a factor in about **10% of large-truck crashes** in the LTCCS, and within that bucket, brakes and tires are the dominant pair.

So when someone says "brakes and tires are the number-one predictor of mechanical truck-crash risk," the precise version is: among *vehicle* factors, brakes are the single most common and most crash-causal, and tires are the next. That's exactly what the federal data shows.

What the inspection blitzes show — every single year

The second, independent data source is enforcement. Every year the **Commercial Vehicle Safety Alliance (CVSA)** runs **International Roadcheck**, a 72-hour blitz where inspectors across the U.S., Canada, and Mexico conduct tens of thousands of inspections and publish exactly which violations put vehicles out of service. It's the closest thing the industry has to an annual physical for the fleet.

The result is monotonously consistent: **brakes top the out-of-service list, year after year.** In the 2025 Roadcheck, inspectors conducted 56,178 inspections; **18.1% of vehicles** were placed out of service. Among vehicle violations, **brake systems alone accounted for 24.4% of all out-of-service violations**, and when you add brake-adjustment violations, **brake-related issues made up more than 40% of vehicle OOS violations.** CVSA cares about this so much it runs a *second* dedicated event — **Brake Safety Week** (Operation Airbrake), scheduled for August 23–29, 2026 — focused solely on brake condition and maintenance.

Tires are right behind brakes as a perennial top OOS category. Federal rule **49 CFR 393.75** sets the floor most operators forget the specifics of: a minimum tread depth of **4/32"** on steer-axle tires and **2/32"** on all other commercial tires, with any tire showing exposed body ply or belt material prohibited from service outright.

Two independent data sets — crash investigations and roadside enforcement — and they point at the same two systems. That convergence is why brakes and tires deserve the attention.

Why brakes and tires, specifically?

It's worth understanding *why* these two dominate, because the reason connects directly to carrier risk.

Brakes and tires are the systems that **wear continuously, fail gradually, and are expensive and time-consuming to maintain properly.** A tractor-trailer can have dozens of brake chambers and eighteen tires; keeping all of them in spec requires real money and real downtime. They're also the systems most directly punished by the economics of running cheap: a carrier under rate pressure defers a brake job or stretches a tire past its tread life, and the truck keeps running — right up until a downhill grade or a hot highway says otherwise.

That's the thread back to everything else in carrier safety. The corners that make a carrier dangerously cheap are very often *brake and tire corners* — and those corners surface in the data long before they surface in a crash.

Where this shows up in a carrier's record — before the load moves

Here's the part that matters for brokers and shippers, and the reason this isn't just a maintenance lecture. **Brake and tire neglect is visible in a carrier's public FMCSA profile at screening time.** You don't have to inspect the truck yourself; the roadside inspectors already did, and the results roll up into two signals:

• The Vehicle Maintenance BASIC. This is the CSA category built directly from brake, tire, lighting, and defect violations found in inspections. A carrier in (or near) Alert status on Vehicle Maintenance is, in large part, a carrier with a brake-and-tire problem.
• The vehicle out-of-service rate. Since brakes and brake-adjustment alone are 40%+ of vehicle OOS violations, a carrier's vehicle OOS rate — read against the national average — is, functionally, a brakes-and-tires gauge. A carrier running well above the national vehicle OOS average is telling you where its maintenance dollars aren't going.

Both of these are exactly the signals a careful screen captures. In DOTScreener, the Vehicle Maintenance BASIC indicator and the vehicle out-of-service rate (compared to the FMCSA national average, and read against the carrier's actual inspection count so a tiny sample doesn't mislead) are part of every carrier screen — surfaced, scored, and frozen into the dated record. When a carrier's vehicle OOS rate is double the national average, the screen flags it and notes it on the file; that elevated rate is, more often than not, the statistical shadow of deferred brakes and worn tires.

That's the honest tie-in: DOTScreener doesn't inspect the truck, and it doesn't predict which specific brake will fail. What it does is **surface and document the FMCSA maintenance signals** — the Vehicle Maintenance BASIC and the vehicle OOS rate — that the LTCCS and the CVSA blitzes both identify as the leading mechanical risk, so that "this carrier had a brakes-and-tires problem visible on the public record" is something you saw *before* you tendered, and can prove you saw.

The takeaway

Brakes and then tires are the mechanical failures behind a disproportionate share of the deadliest truck crashes — that's the consistent finding of both FMCSA's crash-causation research and a decade-plus of CVSA inspection data. They're also the maintenance corners cheap operations cut first. The good news for anyone selecting carriers is that the neglect is measurable in advance: it lives in the Vehicle Maintenance BASIC and the vehicle out-of-service rate, free and public, on the day you screen.

Check those two signals on every carrier, read them against the national averages and the inspection count, and keep the record. The trucks most likely to lose their brakes on a grade are, with real statistical regularity, the ones whose FMCSA maintenance data was already waving a flag.

— Mason Lavallet

Founder, DOTScreener.com

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Sources

• [FMCSA — The Large Truck Crash Causation Study: Analysis Brief](https://www.fmcsa.dot.gov/safety/research-and-analysis/large-truck-crash-causation-study-analysis-brief) — brake problems coded for ~30% of trucks; ~170% higher crash-causation likelihood
• [FMCSA — Report to Congress on the Large Truck Crash Causation Study](https://www.fmcsa.dot.gov/safety/research-and-analysis/report-congress-large-truck-crash-causation-study) — vehicle failure a factor in ~10% of large-truck crashes
• [CVSA — 2025 International Roadcheck Results](https://cvsa.org/news/2025-roadcheck-results/) — brakes 24.4% of vehicle OOS; brake-related >40%; 18.1% of vehicles OOS
• [CVSA — 2025 Brake Safety Week Results / Operation Airbrake](https://cvsa.org/news/2025-bsw-results/)
• [NHTSA — Tire-Related Factors in the Pre-Crash Phase (DOT HS 811 617)](https://crashstats.nhtsa.dot.gov/Api/Public/ViewPublication/811617)
• [49 CFR § 393.75 — Tires (federal tread-depth and condition standards)](https://www.ecfr.gov/current/title-49/section-393.75)
• [FMCSA Safety Measurement System — Vehicle Maintenance BASIC](https://csa.fmcsa.dot.gov/)
• [FMCSA SAFER Company Snapshot — vehicle out-of-service rate vs. national average](https://safer.fmcsa.dot.gov/CompanySnapshot.aspx)