Air powered cars

Theres a new bread of air powered hybrid cars coming.  The idea is for the petrol engine to dive the vehicle on long runs and it also charges am air tank that will power an air motor (like those things garages use to get your wheel nuts off, only bigger) the air then powers the car on short runs and has no emissions at all.
The only draw back is you need a big air tank in the boot, and it's a potential bomb. Air tanks if over pressured or they fail have tremendous destructive force, so it'll need to be well protected from a crash.