By design and function, urban areas are covered with impervious surfaces: roofs, roads, sidewalks, and
parking lots. Although all contribute to stormwater runoff, the effects and necessary mitigation of the
various types of surfaces can vary significantly. Of these, roads and travel surfaces present perhaps the
largest urban pollution sources and also one of the greatest opportunities for green infrastructure use.
The Federal Highway Administration (FHA) estimates that more than 20% of U.S. roads are in urban
areas.1 Urban roads, along with sidewalks and parking lots, are estimated to constitute almost two-thirds
of the total impervious cover and contribute a similar ratio of runoff.2 While a significant source of
runoff, roads are also a part of the infrastructure system, conveying stormwater along gutters to inlets and
the buried pipe network. Effective road drainage, translated as moving stormwater into the conveyance
system quickly, has been a design priority while opportunities for enhanced environmental management
have been overlooked especially in the urban environment.