The goal of the leaflet is to specify the requirements for an automatic warning system. Such a system aims at: automatic warning of approaching rail vehicles in adequate time, with a high degree of safety, for staff working on or near tracks, reduction of the staff needed for track-gang warning. The leaflet is based on Report, Part 1, of the ORE1 A 124 Specialists Committee. The system consists in an announcement part and a warning part, so designed that each part can operate separately. The system is specified for operation till 200 km/h. It is based on a radio transmission in the 160 MHz and 460 MHz frequency ranges. A system based on the GSM-R frequency range is out of the scope of the present leaflet.