Bridges or culverts shall be constructed at all street locations where flow patterns cross the street and are not intercepted by an underground storm sewer system or appropriate concrete valley gutter. (Note: Valley gutters on public streets shall not be used to convey more than 10 cfs based on a 100-year event.) Such bridges and culverts must accommodate the 100-year design flows based on fully developed upstream conditions. Bridges and culverts must be designed to accommodate the needed driving lanes for cross traffic along with any safety end treatment, protective offsets, guardrail, signs and/or lighting.