To maintain a lasting road surface a good subsurface drainage is needed.  Subsurface drains are installed along the edges of the road. Road drainage removes the excess water from high water table or water that creeps into the base and sub base through cracks,  It is important to control ground water before it reaches the road structure, otherwise it will cause erosion to the base and the reduction of a lasting road, due to buoyancy of materials in the saturated layer and the reduction of friction forces between soil particles.