Liability. It is the problem that will kill any idea that moves liability from the driver to anything else. A fully automated machine? It's the company that makes the machine. In the train scenario, it's the lead driver.
I'd prefer that the vehicles automatically follow, and closely, however I want better roads. We need to add track-like features to our roads for two reasons:
1: Gives automated vehicles a chance and being able to stay in the lane.
2: Gives better stopping performance.
A regular asphalt/concrete road greatly limits how fast a car can stop. We need some kind of a track that will allow us to lower our stopping distance. So many accidents would be avoidable with a decent way to stop quickly (3g-4g deceleration. Previously I'd thought that sucker cars might be the way to go, however those tend to throw rocks around and would have difficulties with our pothole filled roads.