The application relates to passenger transport systems and related methods. The passenger transport system has multiple step units, a comb plate, a monitoring device, and a marking device. The step units are to be moved one behind the other continuously along a predefined movement path during normal operation. The comb plate is arranged at a fixed position relative to the predefined movement path. The monitoring device is configured to monitor an actual position of a currently monitored step unit relative to the predefined movement path and to detect a deviation of the actual position from the predefined movement path by more than an allowable tolerance value and activate the marking device in response thereto. Upon being activated, the marking device is configured to mark the currently monitored step unit and/or a step unit spatially correlating to the currently monitored step unit.