Washington, DC (CNN Business)Self-driving cars are coming. Or so we’re told. But they still face an existential question: When is a self-driving car truly ready to drive on its own?

That will ultimately be judged by regulators such as the National Highway Traffic Safety Administration. But to prep for that ruling, automakers and tech companies are putting cars on roads and, perhaps more importantly, in simulated environments to fine-tune reactions to events seldom found in the real world.

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