Compressed air car? Yep, this vehicle is designed to tootle around town using a compressed air engine. Which means the emissions are? Cool air.
If you think compressed air is a puny power source consider that the US Navy mounted 15 inch compressed air guns on the experimental U.S.S. Vesuvius, in 1888. Today, you can buy a compressed air rifle that fires 6 rounds of 77 grain 9mm ammo at 900 fps.
So, the main limiting factor with compressed air is not power, it is supply, the need to recharge. Well, how about a small, efficient on-board powerplant that runs a compressor to recharge the holding tanks? This could be used for longer trips, typically outside of urban areas. We like it.
We'd like to see regenerative braking added to the mix. Maybe the compressor is electric, powered by lithium iron batteries, recharged by solar panels in the roof, regenerative braking, and as power source of last resort, a small diesel. BTW, kudos to BMW for putting regenerative braking into the 5-series.