General Motors CEO Dan Akerson unveiled a new version of the Chevy Impala last week. The new Impala will run on either gasoline or compressed natural gas. Photo credit: General Motors.

Give General Motors (GM 2.10%) credit: The old dog is working hard to learn some new green-minded tricks.

Under CEO Dan Akerson, GM has stepped up its investment in green cars -- and Akerson has recently been talking about taking on green-car darling Tesla Motors (NASDAQ: TSLA) with an electric Cadillac. But its latest green-car move had a different twist. Last week, Akerson unveiled a 2015 Chevy Impala that will run on your choice of compressed natural gas or ordinary gasoline -- or both, seamlessly switching between the two. Natural gas is cheaper than gasoline and produces fewer emissions, making it both a cost-savvy option and a green-savvy one.

But there's a catch: At least right now, stations that can refuel a car like this are hard to find. The natural gas system will be offered as an extra-cost option on Impalas starting in 2015 -- but who will pay extra for a car that can use a fuel that's hard to get? In this video, Fool contributor John Rosevear explains that GM has an audience in mind for its latest greened-up ride -- and in one little corner of the market, natural-gas-powered vehicles already make a whole lot of sense.