 On June 25 , NTSB tests of the 740 @-@ foot ( 230 m ) long track circuit below the stopped train showed that it did not work correctly , failing to detect the presence of a test train that investigators had placed on it . Hersman said , " These circuits are vital . It 's a signal system . It 's providing information , authorization and speed commands to the following train , " but stopped short of blaming them in this case . WMATA had replaced all 20 @,@ 000 track circuit relays system @-@ wide in 1999 , after a component designed to last 70 years began failing after only 25 years in service , but the agency claims that none of the newer relays had failed prior to this event . WMATA ordered the inspection of all track circuits on its 106 miles ( 171 km ) of track after the NTSB test . On July 23 , the NTSB announced that the track circuit at the accident site had been malfunctioning since 2007 , 18 months prior to the collision , and WMATA has since found six other circuits within the system that have been behaving unusually . WMATA disabled each circuit that could not be immediately fixed and created an online circuit tracking system , similar to its elevator outage tracker . 
