Pavement drainage requires consideration of surface drainage, gutter flow, and inlet capacity. These elements depend on storm frequency and the allowable spread of storm water on the pavement surface. Several decisions are involved in selecting the recurrence interval and spread. The classification of the highway defines the public s expectations regarding water on the pavement surface. Ponding on traffic lanes of high speed, high volume highways is contrary to the publics expectations.
Design speed is important to the selection of design criteria.
At speeds greater than 40 mph, water on the pavement can cause hydroplaning. With higher traffic volume, projected costs of traffic delays and accidents are also higher. The intensity of rainfall can significantly affect the selection of design frequency and spread. Cost considerations make it necessary to formulate a rational decision matrix. Elevation of the highway and surrounding terrain must also be considered when water can be drained only through a storm drainage system.