The Narrow Structure sign indicates a structure, such as a bridge, culvert, underpass, overpass, or similar structures having a clear road width significantly less than the width of the approach road.

Additional warning may b provided by the use of Object Markers (CS-23).

Where the structure has a clear road width of less than 5.0m, thereby permitting only a single lane of traffic, a supplementary tab sign should be added immediately below the Narrow Structure sign.