Amtrak has operated most intercity passenger rail transportation in the United States since May 1, 1971. This list contains serious incidents – those with deaths or more than 20 injuries of passengers or railroad personnel – that have involved Amtrak trains. (It does not include most grade crossing accidents and trespasser strikes that did not cause significant injury aboard the trains.) All serious incidents involving Amtrak are investigated by the National Transportation Safety Board (NTSB); incidents with suspected criminal activity (notably a 1995 wreck in Arizona) are also investigated by the Federal Bureau of Investigation (FBI).