Comment by njarboe

With automated driving systems you can put the vehicles really close together with high speed and get throughput equal to train systems with single passenger cars. These same tunnels can also have vehicles in them with higher density seating (call them buses, if you like). If you put these vehicles close together you get a train. With this system you can have both cars, buses and trains running all in the same tunnel. Charge each by how much space they take up and vary the price so there is never a backup to get on. Seems like a transportation dream come true. Everybody gets the system they want to use.