Sight triangle areas shall be required at intersections and driveways entering public streets, in addition to the specified right-of-way widths, in which no grading, planting, or structure shall be erected or maintained more than thirty (30") inches above the street center line, except for utility poles, street signs, fire hydrants and light standards. The sight triangle is defined as that area outside of the curb line and the straight line connecting "sight points," one located on each curb line or driveway center line at a distance of twenty-five (25') feet or one (1') foot for each mile of allowed street speed limit, whichever is greater, or fifteen (15') feet along the center line of a driveway.