Blocco automatico a correnti codificate (BACC or BAcc, automatic block with codified currents) is a signalling block system used in Italy on railway lines using 3 kV DC electrification. The track circuits used to detect the presence of a train also transmit coded signals to the trains which are used for train protection and cab signaling. Train protection systems that use BAcc are RS4 Codici, RS9 Codici and SCMT.