Paragraph 31

A train driver’s flashing red or flashing white indicator shall be provided on each approach to the crossing. The flashing red indicator shall not be displayed when the flashing white indicator is showing. The white indicator shall only show if on each side of the railway at least one of the intermittent red lights in each of the traffic light signals mentioned in paragraph 20 above is lit, both barriers have begun to descend and the main power supply has not failed. The flashing red indicator may operate continuously or be initiated automatically by the train as it approaches the crossing.