Coded Current Automatic Block - BACC

BACC is a train protection system used in Italy on railway lines using 3kV DC electrification (mainline and regional lines). The term is an abbreviation of Blocco Automatico a Correnti Codificate (Coded Current Automatic Block).

BACC is a simple cab signalling system that requires the driver to acknowledge any change in the aspect of the next signal, continuously monitors the train speed, and computes braking curves according to the train's length, mass, and braking ability.

The information is conveyed by superposition of two amplitude-modulated alternating currents in the rails (with a carrier frequency of 50 Hz and 178 Hz, respectively). Receiver coils in front of the first axle of a locomotive or control car are used to detect the signal.

MERMEC Group monitoring system measures the magnetic field produced by the coded rail currents and analyzes their signal and modulation looking for anomalies of both current source and detectors. Dedicated sensors are installed in front of the first axle of a locomotive or control car in both vehicle directions.

High Speed

Main & Regional

Mass Transit & Light

Heavy-Haul