The Living City

Living City

“How do you make cities more sustainable?” That’s the simple, yet daunting question Northwestern Engineering’s Kimberly Gray heard in 2011 when she answered a phone call from the chair of the business advisory committee for the Asia Pacific Economic Cooperation (APEC).

The gravity of the question was not lost on Gray. After decades of rapid urbanization, coupled with the growing impact of climate change, the need for environmentally sustainable infrastructure that supports equitable and economically prosperous living has never been greater.

But how does one tackle such a monumental task? Kimberly Gray has a plan.


Cities cover only two percent of Earth’s land surface, yet are home to half of the planet’s population. That means 3.5 billion people live in a combined area less than half the size of the contiguous United States.

While migration from rural to urban areas unfolded gradually over the 20th century in post-industrialized economies like the United States, Japan, and Western Europe, demographic shifts are happening today on a scale never experienced before. According to projections by the United Nations Population Fund, five billion will reside in urban environments by 2030.

Asia continues to experience the most drastic boom in population growth. There, urban environments capable of housing hundreds of thousands of people are constructed in a matter of days. These new metropolises, of course, face the same problems that plague many established cities: inefficient public transportation, poorly managed food and energy supply, and the handling of waste.


When that phone call came in 2011, Gray, now the chair of the Department of Civil and Environmental Engineering, recognized an opportunity to draft a plan that could support municipalities in their efforts to construct cities more sustainably. Her inspiration was simple: let’s partner with nature do the work.

“Cities need to transform themselves by operating more like nature,” Gray says. “We need to remake the human use of materials and energy in cities to mimic the closed loop cycles found in natural ecological systems.”

Gray, who has worked to develop technologies that both protect the environment and enhance public health, knew she needed a team with expertise beyond her knowledge of technological infrastructure, particularly in the fields of design and policy. She connected with Douglas Farr, founder of the sustainability-focused architecture firm Farr Associates, and Northwestern Pritzker School of Law professor David Dana, whose environmental law background would guide how to best implement the team’s vision.

“Architects consider the aesthetic side of cities. Lawyers understand policy and how to best implement your ideas,” Gray says. “It was so much fun to be able to collaborate across these disciplines and learn their perspectives throughout the process.”


The team’s urban sustainability blueprint, called the Living City, combines Gray’s familiarity with sustainable infrastructure, Farr’s experience in environmental design, and Dana’s knowledge of the political feasibility of the plan.

At its core, the Living City integrates four interdependent systems that, if adopted, would help a city maximize its sustainability potential:

  • A sensor-based Information System that serves as the “central nervous system,” monitoring and regulating major city functions
  • A synergistic Energy System that harnesses the full potential of wind, solar, and geothermal energy sources while also recycling waste heat
  • An interconnected Water System that recycles wastewater and storm water and uses cisterns and rooftop vegetation to manage stormwater
  • A Land Use and Mobility System that redistributes land resources to preserve functional green space and create denser urban landscapes that encourage walking and mass transit

“You can’t think of these systems in a silo,” Gray says. “Like nature, we envisioned a system of linked resource cycles. Electric automobiles are a major aspect of transportation, but they are also an integral part of the energy system and make the feasibility of renewable energy more likely.”

Where most cities today use materials and energy in a linear fashion — resources are used, and then discarded as waste — the Living City overhauls these practices in favor of decentralized technologies that integrate within natural ecosystems to allow for resource cycling and recovery.

Gray and StudentsWe use many things once or twice and throw it away,” Gray says. “Nature runs on renewable energy and the constant reuse of materials. Even what you think of as waste, like soil, has a function — it supports the growth of new plants.”

While Gray notes the initiatives outlined in their plan aren’t exhaustive, they represent tangible technological enhancements that cities could implement today. Within its sustainable infrastructure, the Living City incorporates a smart grid that regulates home and building outlet plugs when not in use, building rooftops fitted with solar panels and vegetation plots, and a microbial fuel cell wastewater treatment plant that degrades organic waste while producing energy to sustain its own operations.


When Gray’s team presented their vision of the Living City to APEC representatives in 2012, she was confident widespread urban sustainability could be achieved by 2030. She’s less optimistic about her prediction today, but that has not stopped her research efforts, nor weakened her belief that sustainability won’t be achieved without cooperation.

“The path to making our cities sustainable isn’t dominated by technology, but rather human behavior,” says Gray. “We have the technologies to remake our waste cycles and reduce our carbon footprint, but that undertaking requires coordination among political, economic, legal, and social frameworks. That remains an ongoing challenge.”

Despite the obstacles to achieve urban sustainability, Gray points to Portland, Oregon as an American city that has employed economic incentives, education outreach, and regulations to improve sustainability. The city’s urban growth boundary (UGB) preserves surrounding rural landscapes through zoning limits to potential land development. The resulting urban space is noticeably dense, and has helped Portland earn its “20 minute city” nickname; many citizens enjoy a maximum 20-minute commute to work, school, or most businesses.

“Our way of handling resources and waste has provided us with a high quality of living, and sustainability requires fundamental changes that many would find threatening,” Gray says. “There is an assumption sustainable living will undo our quality of life, but the potential is there to improve it.”

For Gray, that potential motivates her to continue to refine and expand upon the ideas in what she refers to as the Living City 2.0.

“There’s an old engineering tenant that says, ‘if it is not broken, don’t fix it,’” Gray says. “I think cities are broken, but they have an enormous opportunity to be reinvented and flourish.”


Doug Farr and his architecture firm, Farr Associates, drew “A Portrait of the Living City,” based on the team’s design to offer a glimpse into how sustainable land, water, and energy practices could be implemented in an urban environment.

View an enlarged version of the Portrait of the Living City

"A Portrait of the Living City" shows how sustainable land, water, and energy practices could be implemented in an urban environment.

INFORMATION SYSTEM: Central Nervous System (top right quadrant)

The Living City relies on a Central Nervous System to manage the primary energy, water, and transportation systems, as well as a wealth of other city functions. Professor Kimberly Gray says the Central Nervous System takes full advantage of today’s smart technologies through the use of sensors placed throughout the city. Data received from the sensors allow the Central Nervous System to serve as a comprehensive information hub that can monitor and optimize resource use. It can also provide real-time feedback to citizens to nudge their behavior along more sustainable paths — alerting them to transportation delays and preferred alternate routes, as well as informing them about personal energy and water consumption in their homes.

LAND USE AND MOBILITY SYSTEM: Skinny Streets (bottom right quadrant)

According to Gray, the road to sustainability begins by first reconciling our relationship to cars. “We currently commit so much of our space to roads. The first step toward making a city more sustainable is to take away from the automobile.” To this end, she and her team include Skinny Streets that run throughout the Living City. These narrow roadways opt for trees and make room for bicycles instead of a second or third lane of traffic and parking. Lessening the emphasis on vehicular travel encourages more citizens to walk, reduces the carbon footprint from automobiles, and commits more land for green space development.

ENERGY SYSTEM: Geothermal Park (top left quadrant)

The connectedness of the Living City’s energy and water systems are reflected in its Geothermal Park. “Open space needs to function as more than just a deterrent for automobile use or simply recreational space,” Gray says. “The Geothermal Park operates as a pivotal component of the city’s energy and water systems.” Above ground, the open park offers space for outdoor recreation, and is also equipped to manage rainwater runoff as part of the Living City’s stormwater management system. Underground, cisterns house excess stormwater and geothermal heat pumps provide energy to meet the demand for hot water.

WATER SYSTEM: Microbial Fuel Cell Wastewater Treatment (bottom left quadrant)

Gray’s current research on urban sustainability expands upon the Living City’s Living System & Microbial Fuel Cell Wastewater Treatment plant, which uses microbial fuel cells to capture energy from the chemical bonds of organic waste. Collaborating with Northwestern Engineering professors George Wells and Justin Notestein, Gray hopes to help develop an urban biorefinery made up of models and technologies that will reframe traditional ideas of waste. “Instead of putting energy into destroying waste — which we do when we ship food waste to landfills — we want to harvest energy from our waste to create locally-tailored closed-loop cycles.”

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