Other participants emphasized that knowledge is necessary but not sufficient to support sustainable urban development. They pointed out that there is built-in resistance within an urban system, whether it is cultural, institutional, or economic. Many participants stressed that economics cannot be overlooked. Insufficient local revenues are a major reason that new ideas and approaches do not get implemented in cities. Some participants countered that economic research itself must improve, to better account for the lifecycle costs and external (especially public health) costs of unsustainable urban development.

Technology Development

The group discussing technological development was asked to consider specific technologies with implications for sustainability. The group also discussed incentives for and barriers to innovation. One recurring theme was the importance of distributed and integrated infrastructure. Most U.S. urban areas are characterized by large, centralized nodes for critical infrastructure such as power and water. However, there appear to be major opportunities for urban areas to adopt decentralized, smaller-scale technologies, ranging from small renewable power generators to neighborhood water treatment facilities. Distributed infrastructure would add flexibility and resilience, and could also be scaled to meet the needs of shifting populations. Moreover, there are opportunities to integrate some of these traditionally separate systems and make efficient use of the interactions among water, wastewater, power, transportation, telecommunications, and the environment (NRC, 2009).

Viewing the city as a natural system is helpful in this regard. At an individual technology level, biomimicry research can be applied to make technologies more efficient based on natural processes, such as passive heating and cooling in buildings. Participants also noted that industrial ecology principles can be applied to make an urban area less wasteful, and as participants had suggested throughout the day, there is a need for additional data to better understand these resource flows and monitor them in real time. This presents two additional needs: knowledge/data management tools for cities as they attempt to integrate information from different sectors, and low-cost monitoring technologies and sensors that would facilitate real-time information and rapid detection of problems. Some participants pointed out that these are areas in which private industry is now devoting more attention, particularly in the context of the “smart grid” paradigm for modernizing electric utilities.

Urban areas are full of manufactured products and materials that, once past their useful life, are considered waste. However, one participant suggested that cities could be thought of as “above-ground mines” if societies would be willing to invest in repurposing or harvesting valuable materials for reuse. Recycling programs have expanded throughout the country in the past decade, and so a next step might be to investigate approaches to recycling larger, durable goods (e.g., hard plastics or construction materials). In addition, many urban areas in the United States are suffering from outdated and crumbling infrastructure. If this infrastructure is replaced instead of continually repaired, there is an opportunity to transition to new materials that are either more durable or at least more resilient and adaptable to environmental stress.

Some participants emphasized that water issues, which have been fundamental to urban development for centuries, tend to be overlooked as energy, transportation, and



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