Autonomous battery electrical vehicles on simple roads might be a lot cheaper, faster, simpler, and more flexible than either railway or this. This project has a high risk of being technically obsoleted by such a thing long before completion.
Unless of course you mean to say that all vehicles on the road should be autonomous EVs before the first stages of CST are finished (sometime in the 2030s), in which case I want to congratulate you on your optimism that that would be "a lot cheaper, faster, simpler, and more flexible than either railway or this".
And of course you could actually mix autonomous and regular traffic as autonomous vehicles get smarter. Like is already happening in parts of the world.
Also, the main issue in cities is not tunneling into a central location but distributing goods all over the city using e.g. cargo bikes, small vans, etc. Many of those are already electric and typically operate from distribution centers on the edge of the cities. Banning regular traffic out of the cities would free a lot of space for that. Some cities are already doing that or at least strongly discouraging car traffic. E.g. London, Paris, Amsterdam, etc. have large car free zones and lots of modern electric delivery vehicles.