I would think there is a bit of a difference when the vehicle can convert from a car to a train by just merging into an existing stream of traffic in seconds. M

I would think there is a bit of a difference when the vehicle can convert from a car to a train by just merging into an existing stream of traffic in seconds. Multi model is nothing like that. Unloading a ship to a train takes days and unloading a train to trucks is also a full day activity. "subways that run on roads". Not sure what you mean here. Underground tunnels that have trains that have rubber tires instead of tracks like the Paris RER? Or trolley cars on rails that come out of the underground(the subway) and then run on the surface (a trolley). The closest I've seen to the Musk idea is in Seattle where the buses go underground in downtown, but can go on the road network everywhere else.