ATO
Automatic Train Operation
Driving automation layer that commands traction and braking under ATP supervision. Typically responsible for station-stopping accuracy, energy-optimized cruising, and door enable signals.
ATP
Automatic Train Protection
Onboard subsystem that supervises train movement and intervenes when speed or position would otherwise exceed the safe envelope. The safety-critical core of any CBTC system.
ATS
Automatic Train Supervision
Central control-room system that supervises the entire CBTC railway: timetable execution, dispatching, regulation, and the operator HMI. Sits above ATP/ATO and the wayside zone controllers.
DCS
Data Communication System
The wireless network that carries train↔wayside data. Most US deployments use 2.4 GHz or 5 GHz licensed/unlicensed spread-spectrum radio with redundant access points along the right-of-way.
GoA
Grades of Automation
UITP/IEC framework defining who is responsible for which train function across five levels: GoA 0 (line-of-sight) to GoA 4 (unattended train operation). Most US transit deployments target GoA 2.
MA
Movement Authority
The signed promise from the wayside to a single train: 'you may proceed up to point X at speed Y.' CBTC's moving-block paradigm gives every train a continuously updated MA.
OBCU
Onboard Controller Unit
Train-resident vital computer running the CBTC onboard logic: ATP supervision, ATO commands, balise reading, odometry fusion, and DCS communication with the wayside.
ZC
Zone Controller
Wayside computer that owns one geographic 'zone' of the railway. Tracks every train inside its zone, generates Movement Authorities, and hands off to neighbor ZCs at zone boundaries.