A component of the track circuit that lost contact with a Metro train moments before it slammed into an idling train last week had been replaced five days earlier and “periodically lost its ability to detect trains” after the repair, federal investigators said Wednesday.
The National Transportation Safety Board reported that an “impedance bond,” a critical component within a track circuit, was replaced on June 17, five days before the June 22 crash between the Takoma and Fort Totten stations that killed nine and injured more than 70 riders. It was the worst accident in Metrorail’s 33-year history.
In its post-crash testing of recorded track data, the NTSB said in a news release, Metro found “that the track circuit periodically lost its ability to detect trains after June 17.” The NTSB is reviewing documentation on the performance of that track circuit both before and after the impedance bond was replaced.
The track circuits are supposed to detect passing trains and transmit speed and distance information to following trains, allowing automated systems to keep the trains safely separated.
An impedance bond provides a path for a traction current running along an electrified railway.
NTSB investigators have been conducting nightly tests on the Red Line track where the crash occurred. Test progress, the agency said, was delayed by some water in underground access areas that made it unsafe for technicians to work on electrical cables until the water could be pumped out.
The ongoing work includes tests of the impedance bonds, wayside cables, and train control system circuitry for the track segment between Fort Totten and Takoma.
The NTSB is planning tests of the track’s sight lines over the July 18 weekend using trains with cars similar to those in the crash. The 125-foot rail streak marks from the crash indicate heavy braking roughly began 425 feet prior to the point of impact, the agency previously reported.
Most on-scene investigation has been completed.
