Here's a sign of the times: Since early last year, investor/economic prophet Warren Buffett has been putting his money into railroads. His firm, Berkshire Hathaway, now owns about 70 million shares of three major freight lines—2 million of Norfolk Southern, 4.5 million of Union Pacific, and a staggering 64 million of Burlington Northern Santa Fe—worth a combined total of almost $7 billion. Bill Gates is on board with an investment of $1.7 billion in the Canada National Railway Company. Why now? For starters, there's the growing demand for oil alternatives like coal and grain, both of which are shipped on trains. Freight cars also use 65 percent less fuel than long-haul trucks. "It became clear to me the competitive dynamics in the railroad business had changed from when I last thought about them," Buffett told cnbc last year.