Parks on top of roads in tunnels
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New public spaces are emerging as cities bury their highways and roads in tunnels. Putting roads in tunnels liberates the space the previously occupied in cities, allowing the construction of parks, fountains, agoras and pedestrian and cycling paths. All around the world, highways are being torn down and waterfronts reclaimed; decades of thinking about cars and cities reversed; new public spaces created.
 Madrid Rio
The Madrid Rio is ten kilometres long, and transforms a formerly neglected area in the middle of Spain's capital. Its creation, in four years, atop a complex network of tunnels dug to bury an intrusive highway, also rejuvenates a long-lost stretch of the Manzanares River, and in so doing knits together neighbourhoods that the highway had cut off from the city centre.
The park belongs to a larger transformation that includes the construction of dozens of new metro and light-rail stations that link far-flung, disconnected and often poor districts on Madrid's outskirts to downtown. The metro has halve commute times to and from far flung suburbs such as Mostoles
Construction on the tunnels began in 2003 and is nearly complete in 2012 and has been constructed in stages.
The project plans were for a suite of modest new bridges, along with the renovation of some great historic ones, amid a variety of green spaces. The park was to be generally informal, low-key and practical, with playgrounds and ball fields and bike paths.
Public grumbling about traffic jams gradually morphed into praise for a new green space.
The official price tag of Madrid Rio is around $5 billion, all but $500 million of it spent to bury the highway.
- More than 40 kilometres of new tunnels were dug
- Countless tons of granite were installed to make paths and fountains
- 8000 pine trees were planted.
- A new, elegantly simple boathouse has been designed
- 19th-century complex of brick and glass buildings, including a derelict slaughterhouse and greenhouse, are now being renovated to house art studios and a dance theatre.
- Wading pools for toddlers that landlocked Madrid parents already fondly call the beach
- A paved plaza large enough to fit a few hundred thousand people.
A decade ago, bringing back the Manzanares River and the neighbourhoods around it sounded impossible. As Madrid Rio proves, the question for big public projects should not be what can't be done. No. It's what can.