Acronyms that Rail Transit OPS and WMATA rail operations use.

ATC – Automatic Train Control. The system which WMATA uses to safely space trains.

ATO –  Automatic Train Operation, A subsystem of ATC which governs the propulsion and braking of WMATA trains.

ATP – Automatic Train Protection, A subsystem of ATC which maintains safe distances between trains, any loss of ATP data and the train comes to a stop

BIE – Brakes In Emergency, a condition in which the air brake system on railroad cars experiences a reduction in air pressure and as a safety procedures fully applies the brakes to prevent a loss of control or runaway train

LOS – Loss of Shunt. When an ATC track circuit, typically ~300-2000 feet in length, fails to properly detect if a train is located in its block.