Although exploring alternative technology for automibiles is really interesting, nobody's come up with an alternative that combines the efficiency of energy storage, delivery and safety that gasoline has.
CNG has proven more economical than gasoline for years. But most common vehicle CNG tanks result in a lower range as the vehicles were not originally designed for CNG.
More info at: http://www.afdc.energy.gov/afdc/fuels/natural_gas.html