The appeals board shall not grant the permit if any of the following are true:
(a) That the owner of the land will not be substantially damaged by locating the proposed structure on his land outside of the lines of the mapped highway.
(b) That, balancing the interests of the public in preserving the integrity of the mapped highway against the interest of the land owner in using his property as proposed to be used, the resulting disadvantages to the State would be unreasonably disproportionate to the advantages to the owner to be derived from so using the property.
(Added by Stats. 1947, Ch. 1451.)