Classification of highway drainage

Highway drainage is classified as follows.

1. Surface drainage: removes the rainwater from the carriageway and the surroundings.
   • Longitudinal drainage: camber and shoulders, side drains (open or covered), catch drains, kerb and channel, gully inlets and storm sewers.
   • Cross-drainage: culverts (pipe, box, slab, arch), causeways, minor bridges, aqueducts and siphons, which carry water from one side of the road to the other.
2. Sub-surface drainage: controls the ground water, seepage and capillary water, using trench drains, interceptor drains, drainage blankets, cut-off layers and horizontal drains.
3. Special drainage (for slopes, hills and rivers): erosion control and energy dissipating structures, drainage of slopes and retaining walls (weep holes), and river training works.

Based on location, the drainage may also be urban (kerb, gully, storm sewer) or rural (open side drains, culverts).