"The Power of One" is a series of stories about people who have helped their companies become more sustainable. (See earlier stories on UL Environment and eBay.) They can't do it alone, of course. But by coming up with a good idea, enlisting the help of others and making persuasive arguments, one person can change a company and, sometimes, more. Today's story is about an invention that is making its way from one man's garage onto the tracks of America's biggest railroad, the Union Pacific.

Mike Iden is all about saving energy, whether he's on the job -- as the general director of car and locomotive engineering for the Union Pacific railroad -- or on his own.

He's the kind of guy who, when he's driving his car, slows down long before he reaches a red light and starts up slowly afterward because he knows that sudden stops and starts waste fuel.

"You're driving like you're running a train," his wife sometimes tells him.

"Thank you, dear," he replies.

Saving fuel is a big deal at the Union Pacific, whose trains have been carrying freight across the western Union States since Lincoln was president. During the first nine of months of 2010, the company spent $1.8 billion on fuel; that's about 20 percent of its costs. What's more, because freight railroads compete mostly with trucks, they like to boast about their fuel efficiency. "Freight trains are almost four times more fuel-efficient than over-the-road trucks and have less impact on greenhouse gas emissions," the Union Pacific says.

I met Mike Iden last spring when I visited Union Pacific in Omaha to report a story for FORTUNE. (See Union Pacific railroad builds the U.S. economy at fortune.com.) Mike, who is 60, has been in the railroad industry for more than 30 years; he's got a B.S. in mechanical engineering from the Milwaukee School of Engineering and a business degree from Northwestern. He's spent a lot of time at the UP working on making locomotives more efficient -- the company owns about 8,000 of them -- as well as reducing their emissions.

Mike is especially proud of his role in inventing and developing what's called the "Genset" locomotive. That's a breakthrough innovation for the UP -- a multi-engine, ultra-low emitting diesel locomotive that's used in railroad yards in cities like Los Angeles, Houston and Dallas where pollution is a problem.

But he got my attention when he told me about another innovation that he's developing -- the one that began in his garage. It began when he wondered if anything could be done to reduce the aerodynamic drag that is created by "double stack" containers, one on top of the other, that sit right behind the locomotive. Here's a photo of the "double stack" containers behind a locomotive.