Some of it is regulatory, but the majority of it is simply all the stuff in the way. The area immediately under cities is crowded and dense with piping and wiring, in older cities. Also, under that there is often more city that was simply built-over.
If you were building from scratch, you could plan nice systems, but trying to redo the area under an existing dense city is incredibly costly.
Some of it is regulatory, but the majority of it is simply all the stuff in the way. The area immediately under cities is crowded and dense with piping and wiring, in older cities. Also, under that there is often more city that was simply built-over.
If you were building from scratch, you could plan nice systems, but trying to redo the area under an existing dense city is incredibly costly.