Remember George Jetson's car made that putting sound? Peugeot to offer Compressed-Air Hybrid Tech.

Compressed-Air Hybrid Tech: Peugeot To Offer In 2016 On Subcompacts

Pretty wild. The benefits being no batteries and a constantly renewable power source...

For small capacities it could make sense...might be a better way to run a KERS-type setup.

UPS allegidly has some inhouse developed trucks that do just that. Under breaking they compress air and under acceleration they use it back up.

In reply to wearymicrobe:

They may very well have air too, but I saw their compressed "hydraulic" fluid demo trucks at a trade show in Chicago '09-ish.

that is just very very clever.. and a lot more environmentally safe than batteries that need to be recycled at the end of the car's life.

The downside is a much lower energy capacity than batteries, lower charge/discharge efficiency, and if it fails you won't have time to run away from the aftermath.

having been around a few air tank failures.. they usually do not explode, but split a seam or a weld

There was a compressed air sports car a few years ago. I seem to remember it was Swiss maybe? It's not around now anyway. I also remember as a kid reading about a boy who invented a bicycle that was powered by a giant compressed spring. Like a clockwork car. Maybe the technology is on the horizon for ideas like that to actually work. Imagine a spring so powerful it would take all night with an electric motor and a lot of gear reduction to recompress it. Maybe the mechanism to resist the spring uncoiling at low speeds could be used to charge batteries.