In Madrid, Spain, when a highway becomes noisy and pollutant, they bury it underground and put a park on top. The New York Times recently featured Madrid Rio, an urban park created on top of a once above ground highway. The article touches on other urban areas turned green as well, but Madrid Rio seems to be one of the most ambitious to date. Creating a greenspace instead of putting more urban development on top of the newly buried road is the interesting long term planning choice. People now have access to a river via the park, instead of creating more office buildings. This use of urban land hopefully provides the type of recreation the residents of Madrid desire, gives access to the river, and connects the city in new ways.
Before and after, making the river more accessible to people rather than vehicles. Picture from http://urbanity.blogsome.com