Metrorail is divided into blocks, which are varying lengths of track. Within each block is a track circuit, which sends information and speed com- mands to trains. Computers are set to maintain a two-block distance between trains.
SOURCE: WMATA | The Washington Post - June 26, 2009
Metro Control System Fails Test Article | A train control system that should have prevented Monday's deadly Metro crash failed in a test conducted by federal investigators, officials said yesterday, suggesting that a crucial breakdown of technology sent one train slamming into another.