The different approaches are rooted in conflicting views of safety and what the public is willing to accept. “It’s almost like asking people before they even really knew what an iPhone was, how the iPhone might change their lives,” said Johanna Zmud, senior research scientist at the Texas A&M Transportation Institute.

Raj Rajkumar, who brought Carnegie Mellon’s autonomous SUV to Capitol Hill two years ago for members of Congress to test-ride, said he is more convinced than ever that introducing safe-driving features — lane-departure warnings, cameras and sensors — gradually is the prudent path. “We are able to drive only because we have common sense when it comes to things we’ve never seen before,” he said. “But computer software does not have that level of cognitive abilities to deal with things it has never seen before.”