This document defines minimum functional and non-functional requirements for developing a Track Warning Systems (TWS) to warn persons during their work on or nearby the track about the approaching of trains or rail vehicles using acoustical and visual TWS-Signals. These systems may also be able to influence the approaching of trains and rail vehicles by stoppage function. This European Standard is applicable: to systems, sub-systems and components within TWS, including those containing software; in particular; to new TWS; to new integrations of systems, sub-systems and components into existing TWS; to modifications of TWS developed according to this standard. For single warning units (e.g. simple electrical horns) it is recommended to use this standard, too. This document does not deal with: hazards during the installation of the TWS caused by trains or rail vehicles on the lines; hazards caused by the improper use of TWS; hazards caused by the improper behaviour of persons working on or nearby the track; CO2-tyfone, human operated pressure signal horns, flags, detonators or machine warning systems according to UIC 644; national safety regulations to plan and operate TWS in track.