List some grade separations between two roadways that happens underground.
South Street underpass and Brooklyn- Battery Tunnel intersect under Battery Park in NYC.
Any more like this?
By which I assume you mean they *don't* intersect (which is true), hence the topic?
Better not get rail lines involved, or you'll have to spend hours on all of the flying junctions on the NYC subway!
As for multi-level underground road tunnels, I've noticed quite a few while browsing around the major Australian cities.
Are there any cases where there is an underground grade separation, but not in separate tunnels? i.e., you can see the one road from the other as you cross over/under, but they're both still in an underground space?