Greenalley_2 Chicago's out to redefine the way you think about alleys.

The city is embarking on a hugely ambitious effort to make its alleyways -- which add up to nearly 2,000 miles -- environmentally sustainable:

Chicago has decided to retrofit its alleys with environmentally sustainable road-building materials under its Green Alley initiative, something experts say is among the most ambitious public street makeover plans in the country. In a larger sense, the city is rethinking the way it paves things.

In a green alley, water is allowed to penetrate the soil through the pavement itself, which consists of the relatively new but little-used technology of permeable concrete or porous asphalt. Then the water, filtered through stone beds under the permeable surface layer, recharges the underground water table instead of ending up as polluted runoff in rivers and streams.

Rethinking alleys could be a great way to make cities more harmonious with the land they sit on. Especially if alleys become a bigger part of the urban landscape.

Photo via Flickr, from ketalady