> Propane has a much higher risk factor than gasoline due to it being a
> vapor
> at ambient temps and its extremely wide flammability range. That is why
> propane is restricted on almost all tunnels and some bridges.

FWIW, gasoline is generally identically restricted WRT tunnels and bridges.
For example the Chesepeake Bay bridge-tunnel limits their transport to
120gal for gasoline, 120lbs (141gal) for LPG. Not trying to downplay the
danger of propane; on the contrary I think people need to understand how
dangerous gasoline can be. Propane builds up to hazardous concentrations
faster, but consequently it also dissipates faster. Gasoline is unlikely to
achieve an explosive mixture at normal temperatures, but consequently it
sits around as a fire hazard of comparable danger until cleaned up. When
either vents/spills onto a hot engine, BOTH will be in gaseous form-- and
gasoline the more volatile with an autoignition temperature of 536degF to
propane's 874degF.

--
John Bange
'90 Vanagon - "Geldsauger"