Within any sight triangle, no grade, vegetation, sign or other object shall be placed or allowed to exceed a height of 30 inches above the adjacent roadway or be placed in such manner as to limit or obstruct the sight distance of motorists entering or leaving the intersection. Said triangle shall be formed by the street lines of such lot and a line drawn between points along such street lines 25 feet distant from their point of intersection, measured along the right-of-way line.