 A side effect of this important safety function is that the headway of any rail system is effectively determined by the structure of the signalling system, and particularly the spacing between signals and the amount of information that can be provided in the signal.Rail system headways can be calculated from the signalling system.In practice there are a variety of different methods of keeping trains apart, some which are manual such as train order working or systems involving telegraphs, and others which rely entirely on signalling infrastructure to regulate train movements.