Unseen Green
Green alleys in Chicago and Montreal are bringing sustainability to the back door.

By Adam Regn Arvidson, ASLA

The humble alley is perhaps the most utilitarian, most neglected, and least loved urban space. Home to garbage cans, garage entrances, and utility poles, these little streets are crucial to the functioning of the cities that have them. They are not, however, typically seen as places for sustainable design. Alleys, though, just like any other hard surface, contribute stormwater to often overburdened municipal sewers, and exactly because of the utilitarian nature of alleys, the water that runs off them is plenty polluted.

This would seem to make the case for considering alleys in any citywide stormwater management plan, but that, in fact, is rarely done. In most cities, alleys are simply pitched to the center, allowing water to course out into the street and the nearest catch basin. Wherever the slopes don’t work quite right, extra water ends up in basements or adjacent yards. Two North American cities, however, are reconsidering their alleys. Chicago and Montreal have been converting these narrow strips of pavement into spaces that infiltrate water, help mitigate the urban heat island effect, and create more usable area for residents. Though the two programs are quite different, they both offer lessons for other cities considering green alleys.

Chicago

“We have a lot of alleys,” says Janet Attarian, “the equivalent of five Midway Airports.” Attarian is project director of the Streetscape and Sustainable Design Program for the Chicago Department of Transportation (CDOT). She says many of Chicago’s nearly 19,000 miles of alleys have developed flooding problems and that all of them drain stormwater into an already overtaxed sewer system. The city, as is well-known, also has an environmental mandate from the mayor’s office. Thus the green alleys program was born. The task: to retrofit aging infrastructure in a sustainable way.

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