A while ago, I read an article about a firm in India (was it Tata?) that was developing a car with an engine that ran on compressed air. This seemed a brilliant idea, after all, air is all around us and is plentiful. Apparently the fuel tank was replaced by a compressed air tank, which held enough for about 150 miles. The tank could be replenished either from a compressed air line, or from a built in compressor that could be plugged in to the mains overnight. The engine was then just a pump of sorts. This seems an elegant solution to cheap, CO-free travel. Why have we not heard more of this? Is it because the large motor-producing firms have gone down their own expensive lines of research, and do not want to know about a simpler, cheaper possibility?