We've never been asked or challenged at any bridges/tunnels anywhere in the US or Canada.
I guess we might have been in violation somewhere when traveling, but weren't aware of it.
Most of our travels don't take us through areas with tunnels, other than the Interstate variety
through the mountains, usually.
It never occurred to us to ask or look for hazmat signs as we don't consider our RV propane as
a hazardous substance. We do notice the commercial truckers hazmat route signs but it never
occurred to us that our propane might be on the list, too.
What if you drive a LPG/NG/Propane powered vehicle?
Here's a couple of threads about the subject from other websites.
Interesting reading, for me at least. When in doubt, take the detour/bridge/ferry.
http://www.popupexplorer.com/forum/inde ... ic=63573.0
http://www.irv2.com/forums/f86/i-95-tun ... 36935.html
http://www.motorhomemagazine.com/boards ... 192100.cfm