Complex sentence: On July 23, 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.
Split into simpler sentences: On July 23, NTSB announced that the track circuit at the accident site had been malfunctioning since 2007,18 months prior to the collision. Metro has since found six other circuits within the system that have been behaving unusually.