Tanks must be turned off to use Chesapeake Bay B&T.
There is a propane hazard restriction on one route through Baltimore that requires going through a tunnel. Can't think of exactly which off the top of my head (it's one of the "95s"), but if you're going through there you'll definitely want to find out ahead of time.
My family got stuck once right at the toll and we had to turn around and go all the way back and around to the right road (ugh).