I've seen a (news?) story about these compressed air cars in the recent past.  Sounds interesting indeed.

It's all about converting some non-mechanical energy into mechanical energy in these cases.  Water wheels were a direct conversion system - moving water (basically mechanical) turned a water wheel which in turn turned a grinding wheel.  The first non-mechanical energy conversion system was steam (ignoring human, horse, oxen power).  Steam is, obviously, boiling water which creates heat and, more importantly, pressure.  It is the pressure (release) that is used to drive the pistons on locomotives so that they move.  This is the same principle used in pneumatic and hydraulic devices.  And the former is!  Compressed air. :)

C makes it easy to shoot yourself in the foot. C++ makes it harder, but when you do, you blow your whole leg off.

 -- Bjarne Stroustrup

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