Many communities are developing around the concept of the 10- or 20-minute walk—the distance to public transportation and commercial cores. Arlington County, Virginia is often cited as a model with major economic development along the route of the Washington subway system. Many people who live in Arlington County do not own cars because they participate in car-sharing programs or use the Metro subway system as their primary means of transportation.

Arlington County reveals the clear advantages of a smart growth development pattern over conventional sprawl, in terms of carbon emissions, land consumption, household vehicle miles traveled, and property values, Dr. Randolph said. Combining affordability for transportation and for housing into one metric makes it clear that auto dependency consumes more household income, leaving less for housing costs. In communities where distances traveled are shorter, households do not need multiple cars, making more financial resources available to cover housing costs.

Armando Carbonell, chairman of the Department of Planning and Urban Form at the Lincoln Institute of Land Policy, discussed scaling issues as they relate to sustainability. He cited a recent report from the Lincoln Institute of Land Policy, Making Room for a Planet of Cities (Angel et al., 2011), which stated that cities throughout the world and over a long period of time have been growing less dense. Rapidly growing cities in developing countries, where most of the urbanization will take place in the next 25 years, will take up twice as much space per capita as cities have taken up historically. There is a gross dedensification occurring even as our awareness of the need for density – and the value we place on it – grows.

Mr. Carbonell said that there are three scales that need to be considered when working toward urban sustainability: global, national/mega-regional, and local. As an example of a global issue affected by urban sustainability, he pointed to climate change. According to the Clinton Climate Initiative, cities cover less than one percent of the earth’s surface, but are disproportionately responsible for causing climate change. A recent policy report from the Lincoln Land Institute found tremendous carbon savings from increasing the intensity of development (buildings and transportation) in an urban setting (Condon et al., 2009). There is also a need to integrate across scales – from building to block to city to region – in order to understand how various factors that contribute to greenhouse gas emissions and climate change operate together, Mr. Carbonell noted (Figure 2-1).



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