Why has natural gas/propane powered cars become more main stream? Natural gas is just as safe as gasoline. It is cheap, plentiful and relatively low pollution.
Converting gasoline vehicles to natural gas is fairly cheap( much less that the federal subsidy for electric cars) and would be the one quick thing to greatly reduce our dependence on oil. It would be a great transition energy source as we move away from carbon fuels to greener renewable sources.
it would not kill cities/states with oil centric economies as gas is produced similar to oil.
Honda has a 2010 natural gas powered Civic for under $25,000 that gets 36mpg/highway.
Nothing but clean natural gas powers the Civic GX, making it nearly free of emissions.