Abstract: An anti-block control system has four identically designed control channels. Safety circuits (8, 8') are also provided for monitoring the system, as are devices for testing the operability of the system. In this test, performed while the vehicle is stopped or when it is started, a test signal is fed into the channels and the effects of this signal are compared, in pairs, at locations of the controller corresponding to one another. A signal train is formed when the comparison is made. In accordance with the invention, two safety circuits (8, 8') are provided, each associated with a pair of channels, and the signals from all the channels are supplied, in pairs, to the safety circuits. The safety circuits include timing elements. During a test cycle, the signal trains in the two channel pairs generated by using the test signal are compared with one another by use of two comparator circuits (23, 23'), and in the case of non-agreement, a warning or switching signal (18, 18', 31) is generated.