More urban is better for the Earth, data shows

Denser, more urban developments tend to generate fewer air and water pollutants and use less energy and resources on a per capita basis, according to research by Eliot Allen of Criterion Planners and Engineers. Allen has created an “Environmental Transect for the New Urbanism” based on extensive research in the Sacramento, California, region. Allen plots environmental performance of specific developments and the region as a whole on Andres Duany’s Transect, a rural to urban classification system for development. How the “Environmental Transect for the New Urbanism” works is illustrated in the accompanying graphic. Values for the rural and urban extremes are determined for the region (in this case, Sacramento). Numbers for individual projects are plotted along the Transect (in this case, two projects of equal size are compared — one a new urbanist infill development, the other a suburban subdivision). Regional values The difference between most urban development in Sacramento (in or near downtown), and projects on the metropolitan fringe is startling. Downtown projects usually achieve densities of 35 dwelling units/acre (net), and are located within a mile of 30,000 jobs and within 400 feet of a public transit stop. Vehicle miles traveled (VMT) per capita is about 10 miles per day. Projects on the metropolitan fringe, on the other hand, may have as few as one unit per five acres, are located within a mile of only 10 jobs and are four to five miles from the nearest transit. VMT is 35 miles per capita daily. All of this has an impact on resources and pollution, and the effect is most extreme in land consumption, where the suburban edge projects can use up to 100 times as much real estate per capita. But there is also a significant impact in all the other environmental categories, e.g., water use and greenhouse gas generation (both up to four times greater on the metropolitan fringe compared to downtown). Two projects compared An examination of numbers for actual projects brings the point home more forcefully. Metro Square, a 46-unit townhome project taking up a single city block, outperforms the 46-unit suburban subdivision called Antelope in every environmental category. Antelope’s auto use and greenhouse gas generation per capita is double that of Metro Square, and the air pollutants are four times higher than in urban development. Despite the fact that Antelope uses three times as much land, it has less public open space and slightly greater impervious surface. Limitations When considering the concept, three issues should be kept in mind, Allen says: 1) The regional values at either end of the Transect are not absolute, but are intended to illustrate dominant patterns in the most and least inhabited parts of a region. 2) Regions are too spatially complex to produce a perfectly linear scale of environmental performance across their geography. In addition to design features, a project’s environmental performance will depend heavily on its regional location and accessibility because much of its environmental impact is travel-based. For example, the best possible new urbanist design may not be able to offset the environmental burden of a remote location that lacks multimodal travel options. 3) New urbanist projects will not always produce superior environmental outcomes in urban settings, and conventional suburban development will not always produce inferior results in suburban settings. This is especially true across environmental categories where a project of either type could excel in water conservation but fail in stormwater management. In effect, each point on the design portion of the Transect could have a dual set of scores on the environmental portion, e.g., best practice versus inferior practice. Rhetorical tool Allen sees his Environmental Transect as a powerful tool to show public officials, laypersons, and even professionals how the form of development determines ecological impact. “It’s a method of organizing the information in a way that is easily comprehendible,” he says. “You put it in front of a layperson and they immediately see what you are doing.” The data presented through the Environmental Transect should not be viewed as an argument for exclusively high-density, intensely urban development, but rather for a range of development across all tiers of the Transect, Allen contends. Especially in suburban areas, public officials have a tendency to exclude the more urban tiers. “This is one way of persuading officials to allow development across the spectrum of the Transect, because they run the risk of having development come to a halt” if environmental regulations are violated, Allen explains. Even for professionals who may be aware of environmental impact research, the Environmental Transect can have an immediate effect. “The cumulative effect (of the data) is kind of startling — it can be very persuasive,” says Allen. The numbers for individual projects and regions are generated by computer modeling, using the best available data from the Environmental Protection Agency and local transportation commissions, Allen explains. Characteristics and locations of the projects are entered in and processed by a software program, called Index, developed by Criterion and used to evaluate hundreds of developments over the years. Allen invites comments on the Environmental Transect. Contact: www.crit.com.
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