It would be easier to put the entire car on a platform that's on rails

Maybe they could then link several of those platforms together. The mechanical linkage would allow them to travel tightly together without complicated software.

Then maybe instead of everyone bringing their own car, there could be a large box on the platform where more people could enter than would fit in a standard car.

Further, instead of tonnes of batteries in a tunnel underground, could we deliver power directly to the rails the platforms run on?

You mean like the train under the English channel?

Enron Musk, prolific inventor of things which have already been invented.

I even have a name for it. I call it the hypertrain.

I look forward to getting cyberrailed on the hypertrain

That's the easiest problem to solve because you control both sides of the interface. Just add whatever you need to both sides to make them co-operate. I suppose the goal isn't only to work in Boring Company's tunnels.

Ever tried to use your phone in a tunnel or underground, Elon?