A lot of compressed air?

Here's a good answer to the problem of vehicle emissions - run cars on compressed air instead. You can see an Australian TV clip showing two such approaches to the idea.The principle is like a steam engine - pressurised gas drives pistons. But it comes from a tank of compressed air instead of a boiler. Air motors are already used to drive power tools and starter motors in some vehicles.The advantages of using air to drive vehicles are numerous: the engines can be light, little heat is generated, tanks can be refilled quicker than batteries and emissions are even cleaner than the surrounding air. It sounds like a great idea.But from the look of the MDI website (the French company that seems to have got furthest with the technology) it is one that has already run out of puff.This Wired article from 2003 touches on why. MDI claimed to have designs that could travel for 120 miles on a full tank of air. But prototypes only made it four and a half - and money to refine them quickly ran out. MDI's claims to have recently signed a deal with Tata - India's biggest car manufacturer - but that doesn't seem to have gone very far either.The other (Australian) company featured in the video above also seems to be fairly quiet. And there's no recent news on the site of this Uruguayan inventor who's working on compressed air engines. The most recent video is from 2005, and although his bike looks cool, it seems a long way from going into production.I wonder if the compressed air car could be rescued though. Maybe some investment motivated by the recent growth in environmental awareness could propel the technology to a par with electric vehicles.Tom Simonite - online technology reporter.