• there are potentially fewer construction methods available given geologic and anthropogenic constraints;
• logistics can be more challenging because of restricted access and addressing worker safety (workers may be great distances from access points); and
• the expertise and time involved from project inception and completion can be great and may include that associated with community buy-in of a project and government compliance issues.
An underground project requires a systems perspective, such as illustrated in Figure 2.1, that emphasizes interactions between interrelated systems including those associated with land use, intermodal transportation, environmental, cultural, and socio-economic systems. This type of approach highlights the unique combination of skills, knowledge, management, and leadership required for successful infrastructure planning, construction, operation, and maintenance for a sustainable urban environment. Figure 2.1 represents a good start to the kind of thinking necessary, but sustainability of engineered systems within urban systems needs to be designed for much greater complexity and adaptability, such as is done for Complex Adaptive System of Systems (CASoS) engineering. CASoS
FIGURE 2.1 A systems perspective toward a foundation of interacting systems (shown at bottom/base of this graphic) that includes land use, intermodal transportation, natural, cultural, and socio-economic systems deliver quality of life and multiple benefits for the long-term. SOURCE: FHWA, 2008.