In assessing lifecycle sustainability, a “triple bottom line” analysis is often adopted that considers the economic, environmental, and social impacts of development. Elkington introduced the basic concepts of the approach in 1994 and expanded on them and introduced the term “triple bottom line” in 1997 (Elkington, 1994, 1997). The approach provides a framework for a multiple objective assessment of complex investments. “Full cost accounting” pursues a similar goal of including a wide range of impacts in decision making, but full cost accounting usually focuses on developing monetary estimates of different impacts. A recent example of this approach was the estimate of external costs associated with energy production (NRC, 2010). However, environmental and social impacts are difficult to quantify monetarily and often are beyond the current state of knowledge about underground development because of lack of attention. Accordingly, this chapter is divided into sections that consider the lifecycle economic, environmental, and social impacts of underground development. This review of lifecycle costs and benefits is consistent with the committee’s task to explore how use of the underground could increase sustainability.
Lifecycle Planning and Assessment
Underground development often involves a relatively long life cycle even when compared with other infrastructure investments. For example, the Circle Line subway in London was originally constructed more than 150 years ago in the mid-nineteenth century (Bobrick, 1981). Although the line has been extended, renovated, and rehabilitated over time, the original investment in underground construction is still paying off and providing travel and other benefits.1 Similarly, underground pipelines can also last for more than 100 years, especially if in situ inspection, cathodic protection,2 and rehabilitation are performed (e.g., MWRA, 2006). However, government and private planning horizons are usually fairly short with respect to the useful life of the infrastructure. Metropolitan and statewide long-range transportation plans, for example, often consider the benefits and costs of investment for only a 20-year horizon (DOT, 2007). Such a short planning horizon means that any benefits from underground development that occur after 20 years are not considered in investment decision making.
Underground infrastructure development involves an initial investment to create usable space that provides benefits over an extended period. Long lifetimes of underground infrastructure may be excluded from analyses performed by those with short planning horizons, just as owner and user costs of renovating surface facilities may be excluded from cost analyses, although they may be quite
1 For example, to provide shelter. London subway tunnels were used as bomb shelters during World War II.
2 Corrosion protection.