Chicago Green Alley Program

With "more miles of alleyways than any other city," Chicago has taken the green to the streets, literally. Chicago has approximately 1900 miles of public alleys – that's almost 3500 acres of paved impermeable infrastructure to cause a number of issues such as flooding, light pollution and heat island effect. Through the use of permeable, high albedo concrete with recycled materials, and energy efficient dark-sky lighting, Chicago is upgrading its alleys, and many of these techniques can be used to upgrade your backyard…

Besides implementing new alley designs for it's own infrastructure, Chicago has developed The Green Alley Handbook to guide people on the principals and benefits of green alleys:

Alley Drainage Improvement through Proper Alley Pitching and Grading:
All alleys, whether they are permeable or not, should be properly graded and pitched to allow water to run to the center of the alley and then flow to the street. This prevents the need for additional sewer infrastructure and prevents adjacent properties from flooding.

Permeable Pavement:
Permeable pavement has pores or openings that allow water to pass through the surface and percolate through the existing subsoil. Permeable pavement comes in the form of permeable asphalt, permeable concrete, and permeable pavers. In areas where soils do not drain freely, permeable pavement can be used in combination with subsurface drainage systems, like pipe underdrains or stormwater infiltration trenches to slow runoff and reduce stress on the combined sewer system.

High Albedo Pavement:
High albedo pavement material is light in color and reflects sunlight away from the surface. With less sunlight absorbed by pavement, less heat is radiated by the pavement. High albedo pavement therefore reduces the urban heat island effect. This reduces cooling costs, helps the survival of urban vegetation, and improves air quality, which can help reduce the symptoms of some respiratory diseases.

Recycled Construction Materials:
Recycled construction materials can be incorporated in a variety of ways in green alleys. Recycled concrete aggregate can be used in the concrete mix and as a base beneath surface paving. Also, slag, a by-product of steel production, can be used as a component of the concrete mix, reducing industrial waste. Ground tire rubber can be used in porous asphalt and reclaimed asphalt pavement in non-porous asphalt.

Dark Sky Compliant Light Fixtures
Energy efficient, dark sky compliant light fixtures are specially designed to direct light downward, focusing light where it's needed. These fixtures can also incorporate the latest technologies in energy efficiency while maintaining adequate light levels. New alley fixtures will also use metal halide lamps, which produce white light, instead of the yellow light produced by the existing high-pressure sodium fixtures. This will help people to be able to distinguish color at night.

For more info visit the City of Chicago Green Alley website or read the Green Alley Handbook.

(Photos: via Chicago Deptartment of Transportation)

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