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What did you do after you caused your first car accident? I commiserated with a burly AAA guy before working up the courage to call my father.

Google’s self-driving car invented a tool to ensure never making the mistake again.

On Feb. 14, one of the company’s several dozen test vehicles struck a bus, the first accident where the autonomous system was at fault. On March 8, a pair of Google researchers filed were awarded a patent entitled “Bus Detection for an Autonomous Vehicle.” The patent details specific image recognition technology that can pick up on the size and color of a school bus, triggering more cautious driving in the robot car.

Actually, this invention was certainly developed well before the bus accident. (Update: The patent was filed in 2014, but awarded last month.) And that accident involved a public bus, not a school one. Still, the patent reinforces how important it is for Google’s car business that its cars are perceived — by consumers and regulators — as totally safe. Imagine the PR nightmare if it had struck a school bus.

During a South by Southwest talk last week, Chris Urmson, director of Google’s self-driving car unit, said the company had implemented some 3,500 tests since the bus bender to ensure that it “won’t happen again.”

(Hat tip to the Future of Transportation newsletter from Stanford’s Reilly Brennan.)