I have personally analyzed the problem of petroleum shortage and have concluded that flexible fuel vehicles are very important. Vehicles that can burn multiple fuels (gasoline, ethanol or diesel, biodiesel) will be more useable in a fuel shortage. They will still be useful for the entire expected operational lifespan, whereas vehicles that burn only gasoline will be decommissioned early, costing people & business great expense. According to the DOE Flexible Fuel Vehicles Program there are currently a number of flexible fuel vehicles already on the market such as the Chevy S-10 and the GM Sonoma, which run on denatured alcohol (E85 fuel) or gasoline, or any combination of the two. They also get good fuel economy compared to other vehicles on the road, and are utility vehicles.

My research indicates that ethanol or biodiesel may be the most viable renewable fuels, since they require lightweight onboard storage tanks, far less massive than those required for hydrogen, Borax, propane, or natural gas. Lightweight storage tanks combined with renewability give ethanol and biodiesel the competitive edge in my opinion. However these fuels all are intended for use in internal combustion engines and this detracts from their usefulness on a large-scale, due to the limited availability of renewable fuel feedstocks, i.e. grain crops, corn crops, etc.

It is an excellent idea IMO to develop a fuel cell that runs on either gasoline, ethanol, or raw vegetable oil that provides double the energy efficiency of an internal combustion engine. For example the introduction of 4-wheel independent electric drive combined with fuel cells and compact, lightweight ethanol fuel tanks eliminates heavy components associated with cars that rely on internal combustion engines for propulsion. For example there is no need for a drive train, no axel, no steering linkages, or braking components. The only moving parts would be the wheels and suspension components. This would make for a very lightweight and fuel efficient vehicle that could make limited domestic ethanol & biodiesel feedstocks sufficient for widespread use. Conventional gas-guzzling internal combustion engines require cars that are built too heavy to achieve adequate fuel economy.