The Wikipedia article shows that passenger trains use about 35% less energy per passenger/mile than the average car. If fuel efficiency for cars rose to 40 mpg (less than a Prius), they'd be equivalent.
Self-driving cars wouldn't need the jack-rabbit acceleration and deceleration characteristics that drive sales of US cars, and so would probably be more efficient even without the heroic technology of hybrids. If we ever got to the point of self-driving taxis rather than owning your own car, right-sizing would drive the efficiencies even further - if you're just commuting by yourself, call for a single-occupant tiny car rather than driving an oversized hunk of metal down the road.