The main signal here is WP55, the Station Starter, but below this is a Rail Gap Indicator (the white triangular plate with three red lights). If this is illuminated it indicates that the Traction Current in the section ahead has been discharged (switched off). The signal below that (WP57) is a shunt signal. If this clears by rotating 45 degs anti-clockwise the train has been cleared to move towards either the sidings at Ealing Common or towards the Central Line. These moves are not carried out by District Line drivers, and are only used for engineers trains.
