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(THE CONVERSATION) It’s been 60 years since the cover of Popular Mechanics magazine gave us the promise of flying cars. But our personal mobility options remain, today and for the foreseeable future, earthbound. Will the promise of self-driving cars be as elusive? In short, no. The dream of taking a road trip in which we pay more attention to a new book or movie than we do to the driving task is well within reach.

Still, we’re not there yet. And people are just beginning to ask a v...