By Tim McLaughlin

Dec. 14 (Reuters) – BNSF Railway, one of the crown jewels of Warren Buffett’s sprawling Berkshire Hathaway conglomerate, calls itself an environmental leader in the U.S. rail industry with the cleanest locomotive fleet in North America.

“When you see our orange locomotives’ and freight cars’ steel wheels moving on steel rails, think green,” BNSF says in its latest sustainability overview.

But the company is the largest player in an industry that has a pollution problem: U.S. freight railroads are a major source of pollution, chuffing out more nitrogen oxide, the primary component of smog, than all the nation’s coal-fired power plants combined, according to a Reuters calculation using government data.

U.S. railroads together produced about 485,000 tons of nitrogen oxid

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