10. The design of all traffic signs shall conform to and have the minimum dimensions of the specifications adopted by the commissioner, except as otherwise approved by the commissioner. Where conditions require greater visibility necessitating a larger sign, standard shapes and colors shall be used, and standard proportions shall be retained, so far as practicable.
This is not to be deemed to prohibit the erection of enlarged bridge type signs or narrow longitudinal type signs suspended from mast arms, over the roadway.