Phil Koopman, a professor of electrical and computer engineering at Carnegie Mellon University, said Mr. Musk needs to show his cars can handle all situations if he wants to claim they can drive themselves. For instance, he wonders if Tesla has a plan for a big truck splashing gallons of grimy water onto a car in a snowstorm, obstructing the cameras.

“The rabbit hole goes pretty deep if you want to make that [full self-driving] argument,” he said.

Tesla already has been offering a system called “Autopilot” that can control cars on a limited basis with constant monitoring by a human driver. On its website, it says the Autopilot system steers your car in its lane and accelerates and brakes automatically for other vehicles and pedestrians in its lane. But questions already have been raised about Autopilot’s reliability after its involvement in three fatal crashes.
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