Blocco Automatico a Correnti Codificate
BACC is an ATP system which is installed in Italy on all lines with top speeds over 200 km / h on the network of Ferrovie dello Stato. The full name is Blocco automatico a correnti codificate, which means something like automatic block system with coded streams.
BACC is a further development of RS4 Codici. That system is used for cab signaling and requires the driver to acknowledge any change in the signal position. In addition BACC compliance with the specified speed and certain braking curves is monitored by an on-board computer in the vehicle engine.
BACC consists of the following parts:
- Two receiver coils on the rails in front of the first axle of the locomotive or driving coach
- A computerized vehicle device for decoding the received signals and the monitoring of speed limits
- A braking action group
- A display and control device in each cab
AC current flows in the rails at a frequency of 50 Hz to this alternating current is superimposed at a frequency of 178 Hz. Both streams are modulated with a frequency dependent on the position signal frequency:
The frequency of 50 Hz is also used by Codici RS4. All codes of which the carrier frequency of 178 Hz is not required to use the same for RS4 Codici and BACC. BACC is therefore backward compatible.
The driver 's position of the next signal and the speed setting will be displayed corresponding to speed code. The system continuously monitors the speed. When excessive speed or the failure to achieve the intended stopping place of the train is automatically braked.
BACC will regard ETCS out as a class B system.