Urban Centers as Environmental Imperative (Part 2)
Urban centers – mixed-use, transit-oriented, and people-friendly – stand among the most promising ways to address mounting environmental challenges. Bustling places, filled with people and rich with amenities, are extremely good for the planet.
A person who lives and works downtowns consumes only a small fraction of the natural resources compared with their suburban, rural, and most other urban counterparts. Urban centers environmental performance tops not only sprawl but also suburban “transit villages” and most other transit-oriented development (TOD).
In Green Metropolis, David Owen writes that on a per-capita basis, the carbon footprint of the typical Manhattan resident is 70 percent less than that of the average North American.[i] This agrees with other research, and reflects the efficiency of infrastructure shared among greater numbers of homes and jobs. In particular, because high-density forms of construction allow individual dwellings to share walls, they consume less heat in winter and need less cooling in summer. The increased energy and resource use attributable to characteristic features of taller buildings, such as elevators and structural systems, pales in comparison to the energy needed to move people between smaller, widely spaced buildings.
Likewise, environmental footprint from car use is reduced dramatically by increased density. The Sierra Club’s leading researcher, John Holtzclaw, notes that “residential density is the variable most effective for predicting auto ownership and driving.” Holtzclaw’s research shows that auto ownership and driving decrease as density increases because density affects the frequency of transit service and the availability of walk-to destinations.[ii]
The average person who lives in a high-density downtown will likely drive one-third as much as the average resident of an urban neighborhood, and about one-eighth as much as the average suburbanite.
Transit-oriented development (TOD) has deservedly received recognition across the planning profession; more importantly, it has penetrated the consciousness of average Americans and their political leaders. But not all TODs are alike. New suburban TODs, with housing surrounding a nugget of retail and a transit stop, require far more natural and financial resources to sustain than do urban centers. Even older suburban neighborhoods, once built around streetcars and now served by buses, do not perform as well as urban centers with higher densities.
Growth in downtowns and other urban centers should be among our highest environmental priorities. High-density, mixed-use centers cultivate a complex web of mutually-supportive activities, which minimizes the demand for energy and other resources.
Urban centers possess advantages similar to mature ecosystems, where diverse plants and animals emerge, and biological processes are increasingly interwoven. Left alone, ecosystems move from having relatively few species toward abundance and diversity. The maturing ecosystem uses sunlight and resources with increasing efficiency, and most-mature “climax” ecosystems produce the greatest amount of biomass possible at a given location.
Climax ecosystems are also robust. Interwoven and mutually-supportive species and activities are resilient to disturbances because biological processes can advance in abundant ways.
The same proposition is true for human settlement. Integrated systems and activities are essential to a sustainable metropolis. By contrast, sprawling, segregated uses are heavily reliant on overextended systems. To sustain a monoculture of single-family homes and big-box retail centers, auto use and its infrastructure consume enormous amounts of energy and materials. Intensive and integrated urban centers offer diverse and interconnected housing, jobs, and conveniences that can efficiently support daily life and sustain continued economic growth.
As Larry Beasley, the former planning director of Vancouver, British Columbia, wrote in Planning magazine (January 2007): “High density with the right infrastructure is probably the only way that we are going to bring our cities’ [environmental] footprints to anywhere near what [scientists] say is necessary.”
In truth, urban density is not the only factor that affects how much people drive. Mix of uses, availability of public transit, and pedestrian friendliness are all correlated strongly with driving rates. But these factors all rely on densities high enough to provide market demand for local shops, boost levels of transit ridership, and help pay for well-designed streets and pedestrian amenities. The co-variance of density with other major factors affecting driving rates has been substantiated by Holtzclaw and others.
Large disparities in carbon generation exist between locations with reasonable alternatives to the car (generally a function of density) and suburban and exurban locations with their bloated levels of gasoline consumption. Organizations like the Center of Neighborhood Technology have developed compelling maps that show how low per-capita greenhouse gas emissions correspond to high-density transit-oriented locations. This means that urban centers and transit corridors present the most environmentally friendly locations for future growth.
Critics dismiss the positive impacts that urban density can have for reducing greenhouse gas emissions. To them, slow rates of new growth mean that we are largely stuck with present auto-dependent development patterns. But demographic trends suggest that demand for denser housing will rise appreciably in the near future. Baby boomers have moved past their child-rearing years, and younger people are having fewer children. During the first quarter of the 21st century, nearly 90 percent of new residential growth will be for households without children.[iii] This trend points to increased demand for housing downtown and in other urban locations. By one estimate, there is such an oversupply of suburban single-family homes today that this market won’t gain strength for another decade.
Extensive construction of new commercial space can also be expected — partly out of growing demand, but also because about 20 percent of all nonresidential space is redeveloped each decade. The math on this means that reconstruction over the next few decades will far exceed what is on the ground today.[iv]
All of this is not to say that growth in downtowns and other urban centers will be easy, but should be considered as an environmental imperative. While high-density development faces challenges, urban centers stand at the apex of place types when it comes to environmental performance.
[i] David Owen, Green Metropolis: Why Living Smaller, Living Closer, and Driving Less are the Keys to Sustainability, Penguin Ltd., 2009.
[ii] John Holtzclaw et al., “Location Efficiency: Neighborhood and Socio-Economic Characteristics Determine Auto Ownership and Use,” Transportation Planning and Technology, Vol. 25(1), March 2002.
[iii] A.C. Nelson, “Leadership in a New Era,” Journal of the American Planning Association, 2006.
[iv] Reid Ewing et al., Growing Cooler: The Evidence on Urban Development and Climate Change, Urban Land Institute, 2007.