materials from other applications (e.g., concrete made from coal fly ash-based geopolymers).

Capturing all costs, such as diminished air quality or those associated with disruption and business losses during street closures, in a comparison of project alternatives remains a challenge and a topic for future research. Although costs may differ significantly among similar projects, discrepancies observed in the cost of a lane-kilometer of roadway in various countries, for example, suggest that investigating the detailed reasons for lower costs in some countries as compared to others would be worthwhile. Understanding such relationships would assist development of a realistic management framework that objectively distributes total costs over infrastructure life cycle. An entire infrastructure management framework could be informed that includes planning, documenting existing conditions, establishing land use requirements (both above and below ground), and issuance of permits for approved underground use (as directed by informed policy).


Observation: Underground infrastructure can safely enhance the lives of millions, but few federal-level safety regulations exist to guide operational safety at a time when underground system complexity is increasing.

Conclusion 9. Greater user acceptance and occupancy of underground infrastructure and facilities are likely if underground spaces are planned with more consideration of utility, ease of access, wayfinding, safety, and aesthetics.

Potential actions:

a. Develop and adopt performance-based safety mechanisms and codes that not only account for today’s underground occupancies (e.g., mixed use, multi level) and risks, but also allow for expansion and change of use. The International Code Council technical requirements, applicable National Fire Protection Association standards, and other related standards and guidelines could be expanded and made applicable to underground facilities.

b. Incorporate human factor and complex systems engineering concepts to guide threat recognition and technical and operational decision making for normal operations and for operations during times of stress (e.g., in response to extreme events).

c. Incorporate behavioral science, training, biology and physiology, human performance and capacity into safety codes and design.

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