Visibility at intersections. No object, including, without limitation, fences, hedges, trees and other plantings, buildings, structures, walls, signs and motor vehicles, exceeding a height of three feet as measured from the lowest elevation of the center line of any abutting street, shall be temporarily or permanently placed, erected, installed or parked within the clear sight triangle required on a corner lot. The required clear sight triangle on a corner lot shall be determined as follows: The street lines abutting the corner lot shall form the legs of the clear sight triangle. Each of the legs shall extend a distance of 30 feet from the point of intersection of the street lines abutting the corner lot. The hypotenuse of the clear sight triangle shall be formed by drawing a straight line joining the legs at their farthest point from the vertex of the triangle. (See illustration in Appendix A.)