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What does ‘inevitable accident’ mean?

An accident scene. Stock photo by Getty Images

“Inevitable accident” is a defence used in motor vehicle accident lawsuits.

Many negligence suits depend on the “but for” condition, meaning “but for (or ‘if not for’) the defendant’s negligence or carelessness, the accident wouldn’t haven happened.”

Inevitable accident, however, isn’t caused by negligence, but couldn’t be anticipated or prevented by any reasonable care. It’s caused by factors beyond anybody’s control, meaning nobody is liable.

That said, there are two types of inevitable accident defences, sometimes distinguished by different names: inevitable accident and explanation.


Explanation applies when the primary cause of the accident is an “internal” issue, meaning it relates to the driver or their vehicle. That could include a seizure or malfunctioning brakes.

Defendants have to meet a high evidentiary standard for this defence, proving that the accident still couldn’t be avoided even with the greatest care and skill.

Medical conditions are a common explanation defence, but they’re not readily accepted. For example, a 1993 case Perry v. Banno saw the defendant attribute the crash to sudden unconsciousness while driving. His wife said he’d been unresponsive and made no effort to avoid the crash. The court rejected his defence though, saying there’d been no identified cause for the unconsciousness and medical evidence shows that people don’t instantaneously pass out without warning.

Similarly, drivers with existing medical conditions generally can’t use that as an excuse, because courts generally find the driver could have anticipated the event causing them to lose control.

Inevitable accident

Inevitable accident occurs due to external factors like poor weather conditions or an animal on the road (or, in one unusual case, an animal in the car; a bird flew into a car and struck the driver in the head)

There’s a lower threshold of evidence for external claims. The defendant just has to show the collision still could have occurred reasonably without negligence.

Read more:

No negligence defences in motor vehicle accident cases

The "inevitable" accident defence