Brand Avenue: Back Alleys Up Front

The City of Chicago has unveiled a far-reaching and thoughtful plan to "green" its back alleys--all 1900 miles of them. Overlooked but essential components of the city's urban grid, the soon-to-be transformed alleys constitute one of the biggest streetscape overhauls in the country, ever:

If this were any other city, perhaps it would not matter what kind of roadway was underfoot in the back alleys around town. But with nearly 2,000 miles of small service streets bisecting blocks from the North Side to the South Side, Chicago is the alley capital of America. In its alleys, city officials say, it has the paved equivalent of five midsize airports.

Part of the landscape since the city began, the alleys, mostly home to garbage bins and garages, make for cleaner and less congested main streets. But Chicago’s distinction is not without disadvantages: Imagine having a duplicate set of streets, in miniature, to maintain that are prone to flooding and to dumping runoff into a strained sewer system.

The new surface consists of two parts: a porous concrete grid above, and a stone filtration layer below. While the porous concrete was formerly more expensive than traditional concrete, it is now cheaper due to increased production. As such, the price of the porous concrete grid plus the stone filtration layer is now roughly equal to ordinary concrete.

“The question is, if you’ve got to resurface an alley anyway, can you make it do more for you?” said Janet Attarian, the project’s director. 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....

The new pavements are also designed to reflect heat from the sun instead of absorbing it, helping the city stay cool on hot days. They also stay warmer on cold days. The green alleys are given new kinds of lighting that conserve energy and reduce glare, city officials said, and are made with recycled materials. The city will have completed 46 green alleys by the end of the year, and it has deemed the models so attractive that now every alley it refurbishes will be a green alley.

Aside from the obvious environmental benefits of such a plan, it's interesting to consider how making these behind-the-scenes moves can enhance the whole city at a greater scale. Imagine if all of those miles of newly cleaned up and redesigned alleys were places people actually wanted to be: not just a place for trash pickup, but a complete set of secondary public spaces, interwoven with the urban fabric. An exponentially expanded public realm.

Download the gorgeously illustrated Green Alley Initiative planbook: (pdf) (via)

Attention paid to the alleys begs the question of what new functions they could host, and the densification efforts of Toronto and Santa Cruz come to mind. In Toronto, one estimate puts the amount of units that could be added if the city's 2,433 alleys were all opened to residential construction at roughly 6,000. Surely allowing development along a fraction of 1,900 miles of alley in Chicago could yield a significant number.