Define highway drainage

Highway drainage is the process of removing and diverting surface water and sub-surface water from the road and its surroundings, by a system of structures and channels, so that the pavement and the subgrade stay stable, dry and safe for traffic.

The drainage system collects rainwater falling on the carriageway, shoulders, slopes and the catchment above the road, and transports it to a safe outlet. It has three parts:

• Surface drainage (camber, side drains, catch drains)
• Cross drainage (culverts, causeways, minor bridges)
• Sub-surface drainage (control of water table, seepage and capillary water)