Can trains, subways be protected from terrorists

The government's top security officials say they are upgrading subway and rail defenses against terrorist attacks throughout the country, but a USA TODAY examination finds gaping holes, including many that may not be possible to plug.

The holes in security leave travelers more vulnerable on the more than 4 billion trips they take by subway and rail each year than in the sky, where airlines carried fewer than 700 million passengers from U.S. airports last year.
Six terrorist plots targeting U.S. subway and rail systems have been exposed since the Sept. 11 terrorist attacks, and the systems remain a target, transit authorities, security experts and members of Congress agree. An alleged plot to simultaneously bomb four Washington, D.C., Metro subway stations was foiled in October, and another plot to detonate explosives in New York's subway system was averted last year.