Now, PSA Peugeot Citroen is studying a compressed air hybrid system that it might soon offer in one of its subcompact hatchback models. Peugeot isn’t the only manufacturer looking at hybrid-air technology. Ford explored the concept for use on some of its bigger truck models. But as a statement from Paris indicates, the European maker is seriously moving ahead on a technology that would skip costly batteries and, it contends, might be able to deliver fuel economy nudging into the 80 mile per gallon range.