The Madrid train bombings have raised the level of vigilance and foreboding in hard-to-protect major U.S. rail systems, with more security announcements and patrols by armed police and sniffer dogs. From New York to Washington, Chicago and San Francisco, Thursday’s attacks on commuters in the Spanish capital underscored U.S. officials’ unease that trains and subway systems are too expansive and accessible to be secured like airports. “Just as it’s impossible to seal off other places of public assembly, like shopping malls, theaters, sports venues, restaurants, ground-based transportation can’t be sealed off with security measures and continue to operate,” said Cliff Black, spokesman for Amtrak national rail network. Full Story