How long must signalling battery backup last?

For active level crossings, the most quotable Australian figure is from ARTC ESC-03-01 clause 5.3: batteries must operate the level crossing protection, control and train detection equipment, plus any signalling fed from that location, for a minimum of 48 hours with 10% residual capacity under average traffic densities. Note two subtleties that affect sizing: the 48 hours covers the whole location’s load, not just the flashing lights, and the 10% residual means design capacity is effectively 48-hour load ÷ 0.9 before temperature and ageing derating. For other signalling assets, run time is project-specific, ARTC’s signalling power standard states it is defined for each project in the functional specification.