This Dual Carriageway supplementary plate is sometimes used in addition to supplementary plates 502 STOP 100 yds or 503 GIVE WAY 50 yds. It indicates that the road ahead turns into a dual carriageway or crosses a dual carriageway.

This sign is normally used alongside sign face 501 and should never be used on its own. When buying this sign you can select the X height of the text required, this will impact the overall size of the sign face.