Going right a long with edward t, There is the "Fear' issue people have with the thought of a tank of pressurized flammable gas in the car and the issue of "refiiling"
E-85 ethonal vehicles dubbed "Flex-Fuel" are great but fuel stations are limited to larger cities.
Lp or CNG powered vehicle owners would be faced with an even bigger problem.
I have seen many companies use LP powered vehicles mostly
light to medium duty trucks and vans, but they have a fueling station on site.
The idea in theory is good but too many other obsticles would have to be dealt with, mainly refueling.
I am all for Lp or CNG fuel cars, but the general public will have to be educated as to the benefits and be able to refuel there cars in a simple, safe and "Convienient" manner or they will not consider it.