Comment by bombcar

More importantly, there's huge tracts of land that could be new cities.

In the past, we had that incidentally or almost "accidentally" as new industries would create or vastly expand existing towns, and development would occur around them.

Now most "work" is more fluid, and doesn't build company towns, instead you get endless suburbs expanding off an existing city, even when they're technically their "own legal framework".

Even after we moved off the "factory town" type new cities, the suburb development wasn't a major issue because each new exurb usually involved a new highway direct to the city center - but new highways have been rare mainly because all the "reasonable" ones have been built now.

You could either create demand for cities somehow (look at Las Vegas, built out of nowhere) or you could use high-speed commuter rail to empty areas to give room for a seed to grow.