On a corner lot which abuts a state maintained right-of-way or private right-of-way in any district, no planting, structure, fence, wall or other obstruction to vision more than three feet in height shall be placed or maintained within the triangular area formed by the intersecting street right-of-way lines and a straight line connecting points on such street lines, each of which is twenty-five feet distance from the point of intersection. On all rights-of-way proper setback for vision clearance shall be determined by the Zoning Administrator, but in no case shall the requirement exceed that above. (11-20-75, art. 3, 3.09)