I live in S.E Pa and use the Pa Turnpike all the time and NEVER turn off propane. My understanding is most tunnels under mountains either are on a hill of some sort or are crested in the middle of the mountain, such that any propane leaks would travel "down hill, where as in tunnels under bodys of water the low point is usually in the middle which is where the propane would collect. That's the reason why propane is prohibited in Baltimore tunnels.
"DON'T FORCE IT - GET A BIGGER HAMMER'
"Paul & Laurie"
2013 Columbus 340 RK
2013 F350 Dually 6.7 Diesel