So why “just update” the highways to operate like a train network, instead of just building a train network? What benefits will autonomous highways bring which

So why “just update” the highways to operate like a train network, instead of just building a train network? What benefits will autonomous highways bring which normal traditional (or even automated) trains don’t? If you are suggesting we update all but minor streets, it is actually not that simple, since we have to think about pedestrian crossings, bike lanes, parked delivery vans, emergency vehicles etc. Accommodating dumb self driving cars will have to be at the cost of access for all other modes, and that will never happen outside of highways. And if we are going to be spending a bunch of money on intercity travel infrastructure, a well served train line is always a better choice.