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 (NYSE:GM) 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.

Fool contributor John Rosevear owns shares of Ford and General Motors. You can connect with him on Twitter at @jrosevear.  The Motley Fool recommends Ford, General Motors, and Tesla Motors and owns shares of Ford and Tesla Motors. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.