On a corner lot, there shall be provided an unobstructed view across a triangle formed by joining points measured 20 feet along the property line from the intersection of two streets or 15 feet along both the street and alley line from the intersection of a street and alley. Within the triangle there shall be no sight-obstructing or partly obscuring wall, fence, or foliage higher than 30 inches above grade or, in the case of trees, foliage lower than five feet. Vertical measurement shall be made at the top of curb on the street or alley adjacent to the nearest side of the triangle or if no curb exists, from the edge of the nearest traveled way.
