On a corner lot, no fence, wall, hedge or other structure or planting, more than three feet in height, shall be erected, placed or maintained within the triangular area formed by the intersecting street right-of-way lines and a straight line joining said street right-of-way lines at points which are 30 feet distant from the point of intersection, measured along said right-of-way lines. The height of three feet shall be measured above the road surface at the nearest edge of the road traveled. This subsection shall not apply to existing or planting of trees, provided that no branches are closer than six feet to the ground, and that proper visibility is provided.