Mechanical failure causes only a small share of US car accidents, about 2% in the most detailed federal study. Even so, that small share adds up to tens of thousands of crashes, and most of them involve parts you can inspect yourself: tires and brakes.
Car accidents in the US: the big picture
Police reported about 6.18 million traffic crashes in 2024, which works out to roughly 16,900 a day. Of those, 36,297 were fatal crashes. Federal early estimates put deaths at 39,345 for 2024, down from 40,901 in 2023 and the first time since 2020 that the total fell below 40,000.
Driver behavior is behind most crashes. In the federal crash causation study, the driver was assigned the critical reason in 94% of crashes. We break the numbers down in our [guide to how many car accidents happen in the US] and our [guide to the leading causes of fatal crashes].
How much do mechanical failures matter?
The federal causation study looked at crashes from 2005 to 2007 and found that a vehicle component failure or degradation was the critical reason in about 2% of them. Applied to the study’s national estimate, that is roughly 44,000 crashes a year.
Two cautions apply. The study covered towed light vehicle crashes and is now many years old. And the finding looks only at the last event in the chain of causes, so failures that contributed earlier may not be counted. Treat 2% as a floor, not a ceiling.
Which parts fail most often?
Among crashes assigned to a vehicle problem, the largest shares came from two systems.
| Component | Share of vehicle related crashes | Common warning signs |
|---|---|---|
| Tires and wheels | About 35% | Low pressure, worn tread, bulges, vibration |
| Brakes | About 22% | Squealing, soft pedal, pulling, longer stops |
| Steering, suspension, engine and transmission | The remainder | Looseness, clunks, stalling, warning lights |
Tires and wheels
Worn tread, underinflation and damage are the usual culprits. A blowout at highway speed can send a car swerving. Check pressure monthly using the door jamb placard, and replace tires when tread reaches 2/32 of an inch or sooner in wet climates. If you drive a pickup or light truck, our Tire 101 guide to the best tires for trucks explains how to choose the right type and load rating.
Brakes
Worn pads, leaking fluid and overheating reduce stopping power. If the pedal feels soft, the car pulls to one side or you hear grinding, get the brakes inspected immediately. Brake fluid should also be changed on the schedule in your owner’s manual.
Steering and suspension
Worn parts make a car feel loose, wander on the road or clunk over bumps. These problems affect control and raise the risk of a rollover or collision.
Engine and transmission
A sudden stall or loss of power can leave you stranded in traffic. Warning lights, rough running and slipping gears are early signs. Never ignore a flashing check engine light.
How to lower your risk
- Check tire pressure and tread monthly.
- Have brakes inspected at least once a year, or sooner if you notice symptoms.
- Follow the maintenance schedule in your owner’s manual.
- Check for open safety recalls using your VIN with the federal recall lookup.
- Fix warning lights promptly instead of waiting.
Our vehicle repair tools guide covers the basic tools for checking these items at home.
If a mechanical failure causes a crash
- Get to safety and seek medical attention.
- Photograph the scene, the vehicle and any visible damage.
- Keep maintenance and repair records.
- If possible, preserve the failed part rather than discarding it.
- Check whether your vehicle has a recall for the failed part.
- Contact your insurer and ask how your collision coverage
- Consider speaking with a professional about your [car accident legal options], since responsibility can involve the manufacturer, a repair shop or the owner.
This article is general information, not legal advice.
FAQ
How many car accidents are caused by mechanical failure?
About 2% in the main federal study, which is roughly 44,000 crashes a year.
What mechanical failure causes the most accidents?
Tire and wheel problems, followed by brake problems.
How many car accidents are there in the US each year?
Police reported about 6.18 million in 2024.
What is the leading cause of fatal car accidents?
Driver behavior such as speeding, impaired driving and distraction. See our [leading causes guide] for details.