Abstract: The invention refers to a circuit for the busy indication of track sections (1, 2, 3, 4) electrically isolated from each other of a model railway system digitally controlled by a control center (Z). After a controlled digital receiver (E) of an engine determines its own address code with the help of a decoding device, it provides a busy signal via a signal generator (8) to the assigned busy indicator (BM3). To simplify the circuit considerably and to be able to do without the the RF-signal generators so far used in the engine and corresponding RF-receivers of the busy indicator, the signal generator of each engine (A, B) comprises a d.c. source providing a busy signal of a given polarity corresponding to the engine direction on the track as the busy signal to the busy indicator (BM3).