vulnerability to the potentially destructive impacts of climate change throughout the nation (NRC, 2010).

Intensive and well-coordinated use of underground space may be a key component of the sustainability solution. Engineers of underground space will have a vital role in planning, designing, constructing, operating, maintaining, and regulating underground space as well as in informing the social, economic, and even political decisions related to underground space and urban development. Increased interest in underground construction and development is evident throughout the world (Sterling and Godard, 2000). Underground engineering can provide a means to reduce energy use, increase green space preservation, sustainably process and store water and wastes, securely and efficiently site critical infrastructure, prevent and reverse degradation of the urban environment, and enhance quality of life. Many urban areas already enjoy the benefits of using underground space. The I-93 Central Artery and the I-90 extension in Boston (known collectively as the “Big Dig”), for example, although expensive, controversial, and not without problems, have improved peak period travel times through downtown Boston, saving an estimated $168 million in annual downtown travelers’ costs and time (Massachusetts Turnpike Authority, 2006), and have resulted in an enhanced downtown cityscape. Sweden’s experience with underground sewage treatment facilities since the 1940s (Isgård, 1975) and Norway’s expansive network of underground infrastructure, including electric power generation, water supply and wastewater treatment facilities, air traffic control, financial, archival, civil defense and national security facilities (Linger et al., 2002) demonstrate that underground facilities can be both cost-effective and dependable. Montreal began construction in 1962 of its Indoor City, an interconnected network of pedestrian walkways, retail centers, residential areas, and public transportation—about half of which is underground. As of 2006, the structure extended almost 20 miles in length and covered an area of more than 4.5 square miles in Montreal’s downtown core. The project has led to better access downtown, decreased walking distances, and made available additional available public space aboveground (El-Geneidy et al., 2011).

Urbanization is viewed by some as a primary cause of many of today’s societal problems, but it is also viewed as a means to sustainably provide for the populations projected for the 21st century, according to participants in a recent National Research Council (NRC) workshop on urban sustainability research (Shaffer and Vollmer, 2010). While urbanization may not be a root cause, certain problems may have been compounded by it. Participants of that workshop identified a variety of factors that intensify the impacts of urbanization (prodigious consumption of resources in concentrated areas, environmental decline, public health problems, and economic and social inequalities) and reflect the failure of society to recognize urban areas as systems.

Shifting our image of a city from a dense set of autonomous people, structures, and infrastructure facilities to a dynamic system of interdependent elements



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