I recently traveled to Hickory NC and drove through the tunnels on I40 near Tennessee and NC borders and I did not see any signs posted that would prohibit propane use. The only sign I recall seeing is based on explosives transport must use alternate route. I have never traveled with propane on, but do not see any issues. Also, check before traveling and ensure the tunnels are open. I thought they were closing for maintenance...BTW if I am not referencing the tunnels you were planning to travel past, please disregard...Sorry...
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