A culvert conveys surface water through the roadway embankment, away from the highway ROW, or into a channel along the ROW. In addition to the hydraulic function, the culvert must also support construction and highway traffic and earth loads; therefore, culvert design involves both hydraulic and structural design.

Culvert hydraulic design includes determining culvert sizes and grades to handle design stormwater flows. The designer must evaluate the land use to determine the best structure for the location.