According to the intelligence retrieved from Osama bin Laden's compound, Al Qaeda may have been planning on attacking US trains during the upcoming anniversary of the Sept. 11 attacks:
As of February 2010, the terror organization was considering plans to attack the U.S. on the 10th anniversary of the 9/11 attacks. One idea outlined in handwritten notes was to tamper with an unspecified U.S. rail track so that a train would fall off the track at a valley or a bridge, according to a joint FBI and Homeland Security bulletin sent to law enforcement officials around the country Thursday. The al-Qaida planners noted that if they attacked a train by tilting it, the plan would only succeed once because the tilting would be spotted the next time.
Counter-terrorism officials believe that the planning never got beyond the initial phase, and no recent intelligence indicates any active plot for such an attack.