Conscious Choice: Chicago’s Green Alley Program

March 2008 | From the Commish

Chicago’s Green Alley Program

This winter has been a typical one in that we’ve experienced plenty of snow and low temperatures. However, spring is coming fast and that means melting snow and rain. How we manage stormwater is an important piece of the puzzle in terms of being good stewards of the environment and our natural resources. The city’s rain barrel program has generated lots of interest from residents who have begun to look at rainwater as a resource instead of something that is routed through our sewer system.

I want to use this month’s column as an opportunity to introduce you to Commissioner Thomas G. Byrne of the Chicago Department of Transportation (CDOT). Commissioner Byrne will discuss what CDOT is doing to address some of the issues associated with storm water in Chicago.

When most people think about greening and environmental practices, transportation infrastructure doesn’t always come to mind. But as part of Mayor Daley’s expanding collection of “green” initiatives, CDOT has found many ways to incorporate environmentally friendly practices into our transportation planning and public way construction.

By using green infrastructure, landscaping, recycled materials and new techniques, CDOT is helping improve both the built and natural environments.

Our newest initiative is the Green Alley Program. With more than 1,900 miles of alleys, Chicago has one of the largest collections of these access streets in the world. They are critical components of Chicago’s transportation network, providing access to garages, loading docks and storage areas and a place for refuse storage and collection.

But as with any paved surface, alleys also provide the challenge of managing stormwater. Many Chicago alleys were built without a connection to the city’s combined sewer and stormwater system. Therefore, rainwater collects in certain areas and sometimes flows into backyards and garages.

CDOT began the Green Alley Program as a pilot in 2006. The Green Alleys incorporate permeable pavement — either asphalt, concrete or pavers — that allow rainwater to flow through the surface into the ground below. Some alleys include an infiltration basin below the pavement that collects water, then allows it to seep into the ground. These permeable pavements not only help address the issue of rainwater collecting in alleys but also help recharge the underground water table.

CDOT worked with a research team to develop asphalt and concrete mixes that provide the desired permeability while maintaining the durability needed to support garbage trucks and passenger vehicles. Many of the permeable pavements also include recycled material, such as “slag,” a byproduct of metal processing, in concrete. Ground tire rubber, from old automobile tires, was also incorporated into the permeable asphalt.

The Green Alley benefit goes beyond permeability. CDOT also uses “high-albedo” pavers and concrete. These light-colored surfaces reflect sunlight instead of absorbing it, helping keep the surrounding areas cooler and mitigating the urban heat island effect. Other techniques include using proper grading and pitch to facilitate drainage and using dark sky-compliant light fixtures to reduce light pollution, provide uniform illumination and lower electricity costs.

CDOT has installed more that 25 Green Alleys throughout the city, and that number will continue to increase each year. The cost of a Green Alley can vary greatly, depending on the type of solution used, size of the alley, type of subsoil, etc. Currently, the cost ranges from roughly the same as a conventional alley reconstruction to nearly twice the cost. However, as CDOT expands the number of Green Alleys, the materials cost comes down and soon may match that of a conventional alley.

The program has earned industry praise and garnered interest from municipalities across the country. In 2007, the program won the Chicago Innovation Award, sponsored by the Chicago Sun-Times and Kuczmarski & Associates.

The city’s landscaped median program is another visible greening effort. Chicago has more than 90 miles of landscaped medians throughout the city, featuring trees and plants chosen for their hardiness in the urban environment.

Medians provide much more than aesthetic appeal: median trees help improve air quality by removing carbon dioxide, and trees and plants help ease the urban heat island effect. Medians can also help reduce stormwater runoff.

CDOT also recently completed a pilot test of sidewalks made of 100 percent recycled tire rubber. More than 550 feet of sidewalk sections were installed across the street from the Chicago Center for Green Technology. CDOT engineers are currently evaluating the performance of the sidewalks, gauging how they stand up to heat, cold and precipitation.

CDOT continues to pursue these and other “green infrastructure” programs, working toward Mayor Daley’s vision to make Chicago one of the greenest cities in the world.

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