i still think biodiesel has the most promise of the various alternative fuels.
Think systems, man systems! :-) It's a safe bet there are no more 'magic bullet' solutions for any of the problems we have now. Car nuts should wildly support mass public transportation -- lessening freeway traffic even 20% would take massive pressures off petro consumption, greenhouse gas, old-car smog checks, runaway/throwaway care production, etc. Flexible hours and a 32-hour work week (with bennies and living wage) would knock off the peaks, municipal planning in some instances (not all) instead of developer raping/pillaging, etc to lessen transpo need, would all leave room for more fun, less toxic, less contentious car ownership.