If an advisory speed is located within a regulatory speed zone, it is not necessary to lower the zone speed to conform with the advisory speed. In erecting the signs, however, care should be taken not to erect a regulatory speed limit sign so near the advisory speed sign that drivers may become confused by two different speed values.

An advisory speed within a regulatory speed zone should not be posted for a value higher than the posted speed of the regulatory speed zone. Care should also be taken not to place a regulatory speed sign between an advisory speed sign and the location to which the advisory speed applies.