I already made this joke up-thread:

> You might even call such an arrangement a "train"

Joking aside, though, the big issue with trains is last-mile. The road network covers a lot more land than the rail network does, and can reach places that trains can't. And this seems to be inherent to the physics of it, driven (hah) by cars ability to turn where trains cannot.

Mass transit enthusiasts love to gloss over the very real convenience issues that mass transit has, saying "Well everybody should just live next to the train station." The world doesn't work like that. Hence why I think a hybrid system of dockable autonomous vehicles that can be linked up into a train in high-throughput thoroughfares gives you the best of all worlds.