Galvanized steel poles are deemed frangible, but not for cyclists and motorcyclists.

Most road signs are erected on galvanised steel tube posts. These are usually C250L0 (or lighter weight C350L0). They are intended to deform on impact thus minimising vehicle damage and occupant injuries. 

The graph below shows Transport for NSW’s appropriate post size in relation to sign height and sign face area. The shaded area represents posts ‘deemed frangible’ for cars/trucks (C250 grade).

Where there is risk of cyclists or motorcyclists striking the signs, review the need for the sign and if deemed required, a more frangible device would be required to prevent death and serious injury. 

Source: Safe System Solutions Pty Ltd, Illawarra Mercury and TfNSW.