Metro’s alert system continues to fail periodically in the area of track where one Metro train crashed into another last month, killing nine and injuring more than 70 people.

A component of the automatic train alerting system that may have failed to prevent one train from knowing another was stopped ahead on the track continues to flicker intermittently in that same spot even when new equipment is used, National Transportation Safety Board member Debbie Hersman testified Tuesday. The device removed just five days before the crash as part of routine maintenance doesn’t fix the problem, either.