A car that runs on air? It sounds like an environmentalist's dream. Scratch that, it sounds like a dream for everyone outside the fossil fuel industry. The MDI MiniCAT runs by the power of compressed air technology (CAT). No noxious emissions, a tiny carbon footprint, using a cheap, renewable resource. It has a range of about 125 miles and a maximum speed of 70 mph. A fillup at a compressed air station could be as low as $3 and takes 3-4 minutes. The MiniCAT seats three people and has a good-size trunk. See a video report here. MDI Air Cars have been designed in a range of models and sizes, including duel-system cars that can switch to gas power when traveling at higher speeds. The MDI CityCAT has been on the road for almost ten years in taxi cab form.
There are some disadvantages to compressed air propulsion. Compressed air is somewhat less efficient than electricity for running a vehicle. There is a limited range, meaning you'll have to fill-er-up more often than with gasoline, BUT like electricity, a vehicle can be "recharged" overnight, using a home compressor. CAT engines do not produce heat, so an alternate system would be used to heat the vehicle interior. Although the car itself produces no greenhouse gases, the energy used to compress the air may.
Tata Motors of India picked up the project last year, and hopes to have production models for sale in Europe and India sometime in 2008. The MiniCAT is projected to sell for about $7,000, and an all-plastic "People's Car" model being developed for India may go as low as $2,500.