Changes Made to Signal System Before Metro Crash: NTSB

WASHINGTON -- Adjustments were made to the system that detects trains at the site of last month's deadly Metro train crash after a piece of equipment was replaced, federal investigators said.

The process for replacing the equipment before the accident called for changes to the track circuit signal strength, according to the National Transportation Safety Board.

The equipment, known as an impedance bond, communicates information such as speed and distance between the tracks, trains and operations control center.

One impedance bond was replaced five days before the June 22 crash and failed periodically before it. Another was replaced in 2007 and intermittently malfunctioned.

Investigators are looking into whether the adjustments may have affected the system's performance.

Copyright AP - Associated Press
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