Running an "Air Car"

I ran across a link to an interesting article today - a car that runs on air. Seems like an interesting idea to me, of course, there is a cost to generating the compressed air that has to be balanced against the elimination of traditional fuels. The article is at the HowStuffWorks site and talks through some of the challenges. 

The car will only be practicle for short commutes and is focused on city driving at this point, but like all the other ideas out there, a good start.