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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
Part of the landscape since the city began, the alleys, mostly home
to garbage cans 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
What is an old, alley-laden city to do? Chicago has decided to
retrofit its alleys with environmentally sustainable road-building
materials under its Green Alley initiative, something experts say is
among the most ambitious public street makeover plans in the United
States. In a larger sense, the city is rethinking the way it paves
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.
Some of that water may even end up back in Lake Michigan, from which Chicago takes a billion gallons a year.
"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
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. "It is now business as usual,"
But all these improvements come with a cost, and some people around
Chicago have begun to wonder if a city that hardly recycles its trash
and has a hard time keeping its trains and buses running should be
spending money on fancy alleys.
Judy King, putting all her household refuse into one bag on Tuesday
and tossing it into a bin in a green alley, said: "How do you decide
where your priorities are? It's a hard one. I'm bothered that there
isn't more recycling."
The city has begun having serious talks about a comprehensive
recycling program to replace the uneven guidelines now in place. But
beyond recycling, it has a vast array of "green initiatives" that put
it at the forefront of environmentally conscious cities.
This month, the city started two programs with financing from the
Clinton Foundation that are intended to help owners of homes and
businesses to modernize old, leaky buildings to reduce energy
The city also has an expedited permitting process for builders who
use green techniques. Its garbage trucks and street sweepers have
emission-control devices. In recent years, it has installed rooftop
gardens to collect rainwater, planted a half-million new trees and
created more than 200 acres, or 80 hectares, of parks and open spaces
intended to clean the air and add bits of beauty.
As for the alleys, the city says the cost of construction is offset
by what it would have paid for maintenance and sewer improvements for
the old ones.
The new alleys will require maintenance, too, so their pores do not
get clogged, but, Attarian said, "I think they're pretty
The city pays about $45 a cubic yard, or $60 a cubic meter, for
permeable concrete, with the price per cubic yard about $100 less than
it was a year ago when concrete plants were just revving up production
of the new material. Beyond that, there is the added expense of the
stone filtration layer beneath the concrete.
Attarian said ordinary concrete costs $50 or more a cubic yard. The products look pretty much the same.
With its history of heavy industry and bare-knuckled reputation,
Chicago may not seem like the most likely city to exhibit environmental
But Mayor Richard Daley has said that he wants to make Chicago a
green model for the country. A few years ago, he was derided as a
tree-hugger; now, other mayors are copying him. "Global warming is not
a question," Daley said in a recent news release. "How we deal with it
Martin Pedersen, the executive editor of Metropolis, a magazine
about urban living, said, "Recycling programs are all well and good,
but the things that really move public policy and the industry are
things like taxes and the building code."
Pedersen said Daley had "made adjustments to both to encourage green building, and that's a big deal."
In the past several years, Chicago also has built 90 miles, or 145
kilometers, of landscaped medians and refurbished more than 100 miles
Michael David Martin, an associate professor and associate chairman
of the Department of Landscape Architecture at Iowa State University,
specializes in the study of alleys and neighborhoods. Martin praised
what he called "more thoughtful alley design."
"The alley is not only functional," he said, "but an educational
green landscape that is helping a city experiment with design and
different ways to handle water."
"'To be neutral and to be passive is to
collaborate with whatever is going on.' Democracy is not just a
counting-up of votes, but a counting-up of actions.'" ~Howard Zinn
Chicago boasts 1,900 miles of public alleys, the largest system in the world and a prime city asset.
Alleys are fine places to walk a dog, shoot hoops, and stash garbage cans so they don't clutter the sidewalks.
But alleys pose a problem in how they handle water. Alleys are
designed high on the sides and low in the center, so water flows to the
street and into catch basins. But over time, alleys lose their grade,
and water can pool up during storms. Instead of running into the
street, water runs into yards and basements.
The alley can be regraded, or rebuilt with a sewer, but both
solutions add water to a sewer system already burdened during heavy
Alleys also create "heat islands," places that absorb heat, and increase city temperatures.
About four years ago, the Chicago Department of Transportation
sought ways to "expand its toolkit" for alleys, said Janet Attarian,
director of the department's streetscape and sustainable design
program. The CDOT wanted permeable alleys, so that water goes into the
ground, and it wanted alleys that reflect rather than retain heat. And
it wanted alleys that are long-lasting.
The solution, called the "Green Alley Program," uses permeable
asphalt and concrete, developed by engineers who work for the city and
The innovative Green Alley program earned the City of Chicago a 2007 Chicago Innovation Award.
"It was a really great, interesting project," said Attarian, an
architect by training and the program instigator. "Usually, with
impermeable asphalt, water is the enemy. In this way, water is your
The asphalt recycles tire rubber in its mix, and the concrete uses
"slag" -- a byproduct of metal processing -- to make it reflective.
The city now has laid nearly 40 green alleys, attracting interest
from private developers and other towns in Illinois and Canada.
"We've been able to offer solutions that are the most effective from
a cost point of view and a functioning point of view," Attarian said.
The city team hired State Testing Co., a consulting firm, to help develop and test mixtures.
One puzzle centered on making asphalt permeable, but still strong.
Permeable asphalt mixtures rely on fibers for strength, but the fibers
Green Alleys needed were hard to buy. They were costly and, with the
O'Hare Airport expansion roaring ahead, hard to acquire.
City engineers eventually found ground automobile-tire rubber with
its fiber-rich content made an excellent substitute. About 600 tires
can be recycled into a 600-square-foot alley.
The tires turn into a "black juice," replacing some of the oil that
ordinarily goes into asphalt, and the juice is added to gravel and
other material. Bigane Paving of Chicago produced the material on site,
where it was adjusted as it was laid down in the pilot alleys.
The permeable materials are laid over rock beds that contain 40
percent "voids," or empty spaces, out of the total volume, to store
water so it takes longer to get to the sewer. The area under the alley
can thus act as a detention pond -- instead of nice, carpeted basements
playing that role.
Attarian said the project saves money, both because the cost of
materials is going down and because CDOT doesn't always have to
entirely rebuild an alley.
"Maybe there's a section that has a low spot. Instead of having to
regrade all of it, we can put in a permeable center trench and solve
the problem," Attarian said.
About five of the new alleys use lighting that casts light down and out, rather than up, to reduce light pollution.
Attarian doesn't know if all alleys can use permeable materials.
"The original alleys we put on good, permeable soils," Attarian
said. "We want to work on places where the soils are not permeable.
That's something we want to do homework on."