The Shear Joint is for standard street signs ranging from 50NB, 65NB & 80NB sign posts. The
shear joint fails before the post, leaving the post in good order ready for reuse. It improves the chance of the sign post remaining straight so that there is a much higher reusable potential. If the sign is severely damaged the short section in ground may be recoverable in most cases. With the base always left in place and the stub easy to be restored with a new sign top section it makes the cost of repair or replacement a more quantifiable and simple task.
The energy to cause the sign to fail is lower which lessens the sustainable damage and potential injury without reducing the strength of the post to function as a sign. The screws hold the joint in shape and firmly in place to resist actions of the weather and what people can manually apply.
When impact occurs the joint is forced open and the screws will progressively shear and fail, if the impact is not so severe to cause all screws to fail at once there is the potential that the sign will be retained tethered to the base. The natural failure of the joint holds the potential that the sign may stay tethered and not become a projectile. It is not possible to predict all outcomes.