Chicago Green Alley Demonstration Program
Award of Merit: Small Projects
Chicago has about 1,900 mi of alleys—among the most extensive in the world.
The Chicago Department of Transportation sought to optimize the public alley network to improve the environment due to the green orientation of the city’s leadership.
The project’s goals included developing sustainable criteria for alley improvements, identifying ways to use alleys to improve the environment and engaging residents in developing sustainable infrastructure. A Green Alley Handbook was put together.
Eco-friendly designs were developed and tested in five prototype projects. Goals included providing attractive alley improvements; improving the quality of the city’s water supply; reducing the amount of storm water runoff; reducing the urban heat-island effect; reducing the cost of treating sewage; reducing flooding of adjacent properties; reducing energy use; using recycled materials; and diverting waste from landfills.
A Menu of Options
The majority of alleys are paved with concrete and asphalt, translating into 3,500 acres of impermeable surface. The pavement traps heats, contributing to the heat island effect, puts pressure on the stormwater system and contributes to flooding.
A menu of green design elements allowed for flexibility in selecting green techniques:
• Permeable Pavement: Permeable pavement has pores that allow water to pass through and percolate into the existing subsoil.
In areas where soils do not drain freely, permeable pavement was used in combination with subsurface drainage to slow runoff and reduce stress on the sewer system. In areas where the soil has good drainage, permeable pavement allows stormwater to avoid the sewer system altogether.
• Grading and Pitch: Each of the five demonstration alleys were property graded and pitched to allow water to run to the center and flow to the street, preventing the need for additional sewer and prevent adjacent properties from flooding.
• High Albedo Pavement: High albedo pavement is light in color and reflects sunlight away from the surface. As a result, less heat is radiated by the pavement, reducing the urban heat island effect.
• Sustainable Materials: Recycled concrete aggregate was used in the concrete mix and as a base beneath surface parking. A byproduct of steel production, slag was used as a component of the concrete mix. Ground tire rubber was used in porous asphalt and reclaimed asphalt in nonporous asphalt.
• Additional Environmental Impact: Energy-efficient, dark-sky compliant light fixtures direct light downward, focusing light where it is needed. Metal halide lamps produce white light, rather than the yellow light of the existing sodium fixtures, helping people to distinguish color at night.
The project was tested in the 1700 block of West 106th Street; the 2100 block of North Rockwell Street; the 5300 block of North Glenwood Avenue; the 10300 block of South Avenue G; and the 2400 block of North Harding Avenue.
Jury Comments: “This will have a high—and beneficial—impact on the environment. Also, it makes the numerous, unsightly alleys in the city more aesthetically pleasing—a positive social impact.”
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