Ditches. When the depth or velocity of the design discharge accumulating in a roadside
or median ditch exceeds the desirable maximum established for the various highway classifications,
a storm sewer will be required to intercept the flow and carry it to a satisfactory
outlet. If right-of-way and earthwork considerations are favorable, a deep, parallel side
ditch (see Fig. 2.21b) may be more practical and should be considered instead of a storm
sewer. In some cases where large areas contribute flow to a highly erodible soil cut, an
intercepting ditch may be considered near the top of the cut to intercept the flow from the