A. Related Structures: Catch basins, manholes, inlets, frames, and grates shall conform to the Highway Standards Manual and the Standard Specifications for Road and Bridge Construction in Illinois (latest revision). The spacing of pavement drainage structures shall be a maximum intervals of three hundred feet (300').
B. Culverts: The size and capacity of all drainage structures shall be computed using the "Rational Method". The minimum length of culverts shall be at least equal to the distance from edge of shoulder to edge of shoulder, plus four (4) times the vertical distance from the edge of shoulder to the flow line of the culvert, less the flared end section length. No driveway culvert shall have a diameter of less than fifteen inches (15"), and no crossroad culvert shall have a diameter of less than eighteen inches (18"). In no case shall a driveway culvert be less than the width of the driveway, plus four feet (4') on each side of the driveway. Material for crossroad culverts shall be limited to reinforced concrete culvert pipe (RCCP). All culverts shall have approved end protection. Approved grating shall be provided for crossroad culverts and storm sewer end sections.
C. Ditches: Roadside ditches shall be designed based on a 10-year storm frequency and ditch protection shall be provided, if calculations indicate erosive velocities will be reached. A driveway culvert sizing schedule shall be included as part of the approved improvement plans. (Ord. 96-445, 7-2-1996)