This Standard specifies the principles for railway signalling systems and is applicable to heavy railways. This Standard is applicable to systems of safeworking that rely upon train detection systems including track circuits, axle counters, treadles and train-borne positioning systems. This Standard is applicable to power operated signalling systems, including power operated lineside signals and in-cab signals. This Standard is not generally applicable to mechanically operated signalling systems, such as mechanically operated lineside signals, except where the mechanically operated equipment is included as part of a power operated signalling system (for instance, mechanical ground frames that are released by a power operated signalling system). This Standard does not address the processes and competences for the design, construction and implementation, commissioning, monitoring and maintenance, modification, or decommissioning and disposal of a signalling system.