 Shortly after the incident , WMATA General Manager John Catoe stated that the cause was not known but that " the system is safe . " The National Transportation Safety Board ( NTSB ) began an investigation . WMATA and NTSB investigators considered several possible causes , which might include operator error , brake failure , fault in the computerized signal and operation system , or a combination of the three . During rush hour operation , train movement is typically controlled by a centralized computer system , and a separate decentralized system can automatically apply the brakes to prevent a collision . These systems had failed at least once in the past , and the NTSB subsequently identified incompatible specifications , from the maximum deceleration capability of the trains to the deceleration rates used in the wayside system design . The train has a manual emergency brake , which can be applied by the driver in the event of an imminent collision , if the driver can see and identify the hazard with sufficient time to stop . Officials indicated that the manual brake was indeed engaged . It is possible that the brake system failed to perform as designed , or that the operator applied the brake too late . The lead car of the moving train was two months overdue for scheduled brake maintenance . In a press conference the evening of June 22 , Catoe stated that the last car on the stopped train was a CAF 5000 @-@ Series car ( car 5066 ) , which entered service in 2001 , and that the lead car on the moving train was a Rohr Industries 1000 @-@ Series car . WMATA later confirmed that all of the cars on the moving train were 1000 @-@ Series . 
