U.S. railroads, Wall Street favorites for much of the past decade, are slumping into a bear market amid a three-way squeeze from plunging coal, crude-oil and grain shipments. An index of the four largest publicly traded U.S. carriers has dropped 20 percent from its peak in November, paced by Kansas City Southern, as the companies struggle to offset the loss of volumes. They haven’t tumbled this much since 2011. Those difficulties are likely to drag on, leading to the first annual industrywide earnings decline since 2009, as low natural gas prices sap coal demand, U.S. oil drilling slows and harvests return to normal after a record crop. That threatens to crimp a rally that made the group one of the top performers in the Standard & Poor’s 500 Index. “It’s going to be a tough year,” David Vernon, a Sanford C. Bernstein & Co. analyst, said in a telephone […]