I don't think it is necessary to completely give up anything that resembles the family car. If the crops grown really do produce a net amount of fuel for cars and busses, then I don't see any harm done. In that case, running the cars and busses on biofuels would not contribute to global warming.
There are estimates however that suggest that the crop harvesting does not always result in a net fuel production. That is, in some cases fossil fuel is actually consumed, at a net loss, to produce the biofuel. Consuming french fry oil and the like would seem to avoid this predicament somewhat. Does anyone have any figures to present on that one way or the other?

Long term, what needs to be done is to use solar power to run Personal Rapid Transit (PRT). PRT would transport people in 3 person cars to within 1/4 mile of their desination on a network of tracks that would have no stops at intersections.
Slowdowns due to congestion would be much less than with the conventional automobile because the cars could be run by computers at high speeds even in congested areas. Limitations would occur mainly when the stations where people get on and off the system were overloaded with cars. In that case, the cars that
could not unload would continue on around the 1/4 mile loop until they had an opportunity to unload.
This would represent a delay of about 2 minutes at a car speed of 30 mph.