A roadside drainage channel is an open channel usually paralleling the highway embankment and within limits of the ROW. The primary function of a drainage channel is to collect surface runoff from the roadway and areas that drain to the ROW and to convey the accumulated runoff to acceptable outlet points.

Drainage channels must be designed to carry the design runoff and to accommodate excessive storm water with minimal roadway flooding or damage. The design frequency should correspond with the storm drain frequency. Refer to the RDM for details on ditch shape design and side ditches. When the RDM requirements can’t be met, the channel must be enclosed in a storm drain system (see ).

Refer to the HDM for more guidance on the design of channels.