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5
Lifecycle Sustainability, Costs, and
Benefits of Underground Infrastructure
Development
U
nderground development provides opportunities to use available urban
space more effectively, but it requires significant and potentially cost-
prohibitive investment for initial construction as compared to similar-
use infrastructure built on the surface. This chapter summarizes the existing
knowledge about the lifecycle sustainability, costs, and benefits of underground
development.
Literature concerning impacts of underground infrastructure on the lifecycle
sustainability of urban development is relatively scant. More is known about
monetary lifecycle costs and benefits, while less is known about long-term envi-
ronmental or social impacts. Even those studies related to economic benefits and
costs were primarily to inform assessment of alternatives for proposed projects,
such as for the Alaska Way Viaduct in Seattle (Taylor, 2008). Fewer retrospective
studies have been conducted to assess actual costs and benefits of underground
development.
This chapter does not provide a lifecycle cost assessment for any under-
ground works; rather it identifies factors to be considered in a lifecycle assess-
ment in terms of economic costs and benefits throughout the infrastructure life
(construction, operation, and renovation) and environmental and social costs and
benefits. Research that would inform better and more comprehensive lifecycle
assessments is identified.
125
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126 UNDERGROUND ENGINEERING FOR SUSTAINABLE URBAN DEVELOPMENT
LIFECYCLE SUSTAINABILITY ASSESSMENT
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 state-
wide 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 plan-
ning 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 life-
times 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.
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LIFECYCLE SUSTAINABILITY, COSTS, AND BENEFITS 127
large. Similarly, high discount rates for calculating the present value of future
benefits will make those benefits less valuable if provided long into the future.
For example, the federal fiscal year 2011 real test discount rate for a 30-year
planning horizon was established at 2.7 percent (OMB, 2010). With this discount
rate, $1.00 of real benefits received 30 years later would have a 2011 value of
1/1.02730 = $0.45, or less than half. One dollar of benefits received 100 years in
the future would either be disregarded as beyond the planning horizon or would
have a 2011 value of only $0.07.
A long lifetime in itself also may affect planning for future alternatives.
Particular underground development can preclude other uses or make them more
expensive to implement. For example, underground transportation tunnels such
as the Boston Central Artery project required rebuilding and relocating exist-
ing underground utilities in the tunnel right-of-way. Building foundations may
make re-use of their underground locations prohibitively expensive, preclud-
ing new underground parking, tunnels, or other uses in that location. In effect,
underground construction may increase cost and reduce flexibility of options for
alternative future uses. Because most underground facilities are left in the ground
even after their useful life ends, the extra cost or difficulty of re-using the space
continues nearly indefinitely. A comprehensive planning effort would recognize
that underground space is a resource that should be used in the best manner pos-
sible, rather than letting initial uses preclude later uses. Similar conclusions have
been drawn with respect to limiting space debris in orbits around Earth that may
prevent use of those orbits for other purposes (e.g., UN, 1999).
In addition to assessing the life cycle of underground infrastructure itself,
sustainability suggests that impacts of the infrastructure also be considered for
the entire life cycle of a project. Lifecycle assessment “studies the environmental
aspects and potential impacts throughout a product’s life (i.e., cradle-to-grave)
from raw material acquisition through production use and disposal” (ISO, 1997).
Figure 5.1 illustrates a generic supply chain life cycle. For underground infra-
structure, the supply chain would include the various materials and processes
involved in construction as well as inputs such as energy for lighting and ven-
tilation during facility operation. Closure and decommissioning costs would be
included in the disposal phase in Figure 5.1. The landfill phase would be expected
to include the costs of providing an engineered landfill for disposal or any costs
associated with legacy structures underground.
Metrics to use in assessing sustainable development overall, as well as to
assess specific economic, environmental, and social impacts, are still a subject
of widespread debate even without consideration of the special circumstances of
underground development (Jeon and Amekudzi, 2005). Economic impacts are
typically expressed in monetary units, but a variety of impacts may be considered
for environmental and social impacts. For example, Reijnders (1996) suggests
that broad environmental impacts be considered in preparing a lifecycle assess-
ment including:
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128 UNDERGROUND ENGINEERING FOR SUSTAINABLE URBAN DEVELOPMENT
• impact on resources (e.g., use of renewable and nonrenewable resources,
pollution of resources);
• direct impact on nature and landscape, such as through undesirable change
in landscape;
• air pollution and its contribution to climate change, smog, acid deposition,
odors, and deterioration of the ozone layer;
• soil pollution, such as solid wastes added to soil, through eutrophication,
added toxins, and contributions to groundwater pollution;
• surface water impacts, including biological or chemical discharges with
oxygen demand, toxic discharges, surface water warming, and contribution to
eutrophication;
• noise;
• electromagnetic radiation or fields; and
• ionizing radiation.
In many environmental lifecycle assessment studies, environmental impact esti-
mates are limited to only a few critical categories of impacts, such as emissions
of greenhouse gases and conventional pollutants.
Assessing system interdependencies over the life cycle of underground infra-
structure is also an important and challenging part of assessing risk. A variety of
analytic tools exist to aid in risk assessment of individual infrastructure systems
and interactions. These include Bayesian networks, Monte Carlo simulation, and
decision trees (Rinaldi et al., 2001; Haimes, 2004; Weber et al., 2012). Applying
such tools may inform decision making by reducing some of the high levels of
uncertainty associated with different kinds of risk, especially when dealing with
interactions of complex systems.
In this chapter, the committee assembles existing knowledge of the impacts
of underground development, recognizing there are numerous knowledge gaps,
especially because past studies generally took a narrower view of benefits and
costs than is required for a lifecycle sustainability perspective. There is also con-
siderable variation and uncertainty in the performance of underground develop-
ment, especially with regard to extreme events such as earthquakes or flooding.
Moreover, the general advantages and disadvantages for underground facilities
described in Chapter 3 necessitate specific evaluations for each type of use and
site circumstances.
LIFECYCLE ECONOMIC BENEFITS AND COSTS
Increasing population, consumption, density, globalization, communication,
and other trends suggest an increasing complexity for human society (Boyle et
al., 2010). Implementation of technological advancements can have both positive
and negative repercussions. It is important that processes to deliver sustainable
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LIFECYCLE SUSTAINABILITY, COSTS, AND BENEFITS 129
Recycle
Primary/
Secondary
Mine Fabrication Use Disposal Landfill
material
processing
Reuse
FIGURE 5.1 A generic product cradle-to-grave life cycle. SOURCE: Modified from
Hendrickson et al., 2006.
underground infrastructure be carefully designed to limit negative impacts while
gaining the maximum benefit. Indirect impacts of technology advancements also
must be considered. Developing underground space provides the opportunity
to use surface space for other purposes such as green space for parks or other
aboveground development within or closer to urban centers, but quantification
of such opportunities is difficult. Low-impact design of infrastructure systems
that reduces environmental impacts and transportation costs is now being incor-
porated into urban development (TRB, 2009). Compact city trends support an
underground development concept including a wide range of underground facili-
ties that contribute to an efficient but highly livable environment. In this regard,
inherent economic benefits are derived from utilizing the subsurface as part of the
provision of housing, transportation, commercial, industrial, and utility facilities.
Intensive Development and the Compact City
There has been a longstanding debate about the benefits and costs of inten-
sive development in the form of compact cities relative to dispersed development
and urban sprawl (e.g., Ewing, 1997; Gordon and Richardson, 1997). Compact
cities are distinguished by high densities of people per unit land area, a mix of
land uses within neighborhoods, one or more high-density centers of employ-
ment, and careful spatial arrangement or contiguity of land uses (NRC, 2010).
Critics of the compact city note the deleterious effects of more intensive develop-
ment, including increased traffic congestion, less affordable housing, and higher
consumer costs (Gordon and Richardson, 1997; O’Toole, 2009).
A recent NRC study found that compact cities are likely to reduce vehicle
miles of travel and both direct and indirect energy consumption and greenhouse
gas emissions (NRC, 2010). European experience is similar (Schwanen et al.,
2004). Shammin and others (2010) estimated that total energy use is roughly 17
percent lower for urban area residents than for rural or low-density area residents,
even when all purchased goods and services are considered. To some extent, these
expected benefits from compact cities may arise from self-choice of residents
who wish to drive less, but even when attitudinal factors are taken into account,
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130 UNDERGROUND ENGINEERING FOR SUSTAINABLE URBAN DEVELOPMENT
FIGURE 5.2 Boston Central Artery as an elevated structure and as an underground road-
way SOURCE: MADOT, 2012.
less vehicle miles are traveled in compact cities (Handy et al., 2005). Compact
development also may reduce infrastructure costs and development pressure on
green spaces (Ewing, 1997).
However, higher urban density seems to directly correlate with higher levels
of underground space development (Sterling et al., 2012). Many planners believe
that underground development and use could enhance the net benefits of intensive
development. Use of underground space can reduce traffic congestion and the
consumer costs noted by critics of compact cities while simultaneously achieving
the travel and energy reductions identified by compact city proponents. Figure
5.2 shows the Boston Central Artery, which was originally built as an elevated
structure through downtown Boston but was moved underground in the Big Dig
project, resulting in a corridor of open space (NAE/NRC, 2003). The net benefits
and indirect effects on long-term development may be significant even though
they are difficult to assess on a project-by-project basis.
Construction Phase Economic Benefits and Costs
Our current “built environment includes buildings, engineering works, and
infrastructure such as roads, wastewater and water treatment plants, storm water
management systems, power generation facilities, railways, bridges, and even
natural systems such as rivers and harbors” (Boyle et al., 2010). Underground
development provides an opportunity to place many of these facilities in the
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LIFECYCLE SUSTAINABILITY, COSTS, AND BENEFITS 131
10000
Tunnel Cost per Lineal Foot
9000
(Converted to 1995 dollars) 8000
7000
6000
5000
4000 Earth
3000 Rock
2000 Mixed or varying
1000
0 Regression
Linear ( )
68 70 72 74 76 78 80 82 84 86 88 90 92 94 96
Year
FIGURE 5.3 Cost for mining and lining approximately 20 ft. diameter tunnels for the
Washington Metro over the period 1969-1994. SOURCE: R. Sterling, from data supplied
by WMATA (courtesy of Walt Mergelsberg). Reprinted with permission of author.
largely available space—real estate—beneath existing surface developments.
Sterling (2005) describes the importance of urban underground space planning.
Initial costs for underground construction include those related to geological site
characterization and management of geologic conditions, finding and relocat-
ing utilities, potential disruption to existing infrastructure due to utility strikes,
requirements for engineered backfill, and traffic control along a horizontal align-
ment. A nationwide effort exists to use best practices in underground works in the
interest of public safety (CGA, 2008). However, in urban areas, existing struc-
tures constrain practical design of underground facilities. Underground facilities
must accommodate facility design restrictions and land or easement availability
for construction. The time associated with accommodating requirements associ-
ated with environmental and safety regulations also must be factored into con-
struction costs.
Figure 5.3, based on data from construction of the Washington Metro
from 1969 to 1994, shows a decreasing trend line for raw tunnel construction
costs and, equally importantly, a narrowing of the costs range over this 25-year
period. Although project costs are highly dependent on specific circumstances,
for example, the difficulty of installation of specific sections, this graph could
suggest that accumulated knowledge and risk management, investments in
research, and adoption of better technologies and contracting practices over
the period resulted in cost reductions for actual tunnel construction. Are these
cost reductions being seen in the total cost of newer underground construction
projects? The answer is probably “no,” because demands for higher safety
standards and reduced construction risk and environmental impact for newer
projects have increased. In addition, such changes in technical costs may be
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132 UNDERGROUND ENGINEERING FOR SUSTAINABLE URBAN DEVELOPMENT
Cost of Urban Road Tunnels per Lane Mile
(1996 US$)
$200,000,000
$150,000,000
$100,000,000
$50,000,000
$0
a b c d e f g h i j k l m n o
Project Iden er
FIGURE 5.4 Variability in urban road tunnel costs based on data from Australia, France,
Japan, Sweden, and the United States. Each letter on the x axis represents a different
project for which cost data were provided. SOURCE: R. Sterling, from data collected by
ITA Working Group 13. Modified with permission of the author.
masked by the wide range in total project costs seen in worldwide projects. For
illustration, Figure 5.4 depicts data collected during a study of the costs and
benefits of underground transportation facilities undertaken by the International
Tunneling and Underground Space Association (ITA) Working Group 13 (ITA
WG13, 2004). Cost data on road tunnels from 30 cities in 19 countries were
compiled from questionnaire responses and were converted to a common basis
in terms of 1996 U.S. dollars for the cost per lane mile of roadway.
Although these costs vary because of what is counted in each project’s costs,
the variations observed among countries in constructing a lane kilometer of road-
way suggest that it would be worthwhile to investigate the reasons for lower costs
in some countries as compared to others. Although local geology may have a role,
it is not expected to be the only significant reason for the observed variations.
Differences in design standards, administrative review processes, public engage-
ment, and streamlining of design and construction processes may be increasingly
important. Understanding the reasons for varying costs is important so that the
outcomes of projects developed in other countries can be judged according to
standards other than high cost and so that factors contributing to high costs can
be identified and improved.
Various estimates of the length of water, sewer, and storm water pipelines
in the United States can be found in the literature. Table 2.1 lists a total of
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LIFECYCLE SUSTAINABILITY, COSTS, AND BENEFITS 133
approximately 3.7 million miles of pipeline including transmission, distribution,
and private service connections. More than 480,000 km of underground utilities
are estimated to be installed worldwide annually, including water, sewer, gas,
electrical, cable television, and telephone (Najafi, 2005). A significant portion of
this infrastructure is buried beneath paved surfaces in urban environments. Con-
sequently, more efficient and effective installation and rehabilitation of this vast
utility network would provide significant economic benefits due to lower direct
cost and a minimal disruption of this surface environment.
Lane closures due to surface construction and the subsequent detours cause
traffic delays and have an impact on the cost of fuel (CNRC, 2005). Impacts can
be minimized through the selection of suitable construction equipment. Further
savings for initial capital equipment may be realized, for example, with trench-
less methods, especially in horizontal construction because of reduced use of
construction equipment (Woodroffe and Ariaratnam, 2008). In contrast, open-cut
excavation requires the use of numerous pieces of equipment including excava-
tors, bulldozers, surface compactors, and haul vehicles.
Now implemented in underground works are alternative contracting mecha-
nisms that provide innovative means for allocating project risks to reduce their
effects on bid amounts. These include approaches such as design-build, design-
build-own-operate-transfer, and construction manager at risk. Additionally, per-
formance-based specifications are used to promote contractor creativity and
reduce construction costs. Incompleteness of performance-based specifications,
however, may negatively affect the final product.
There is little comparison of the costs of underground versus aboveground
construction (Parker, 2007). Lifecycle cost analyses consider the direct, social,
and environmental costs as well as the costs for specialty items such as heating,
ventilation, and air conditioning systems over the life cycle. Because they are
critical to infrastructure functionality and must be carefully selected and installed
during initial construction, these and other operational costs usually are combined
with direct capital costs in selecting the best construction alternative.
Safety hazards and risks are inherent in all construction projects and need
to be assessed during the design phase. A risk-based safety impact assessment
approach was adopted for the construction of a subway line in Seoul, Korea (Seo
and Choi, 2008). Open-cut construction also was evaluated for comparison pur-
poses. The goal was to identify and reduce, prior to construction, the risks associ-
ated with design items that could cause construction accidents. This is important
because subsurface construction is done “out of sight,” thereby requiring a high
degree of skill and extensive experience on the parts of the designer (often
contractually obligated to provide full-time quality control inspection) and the
constructor. The design and construction of subsurface infrastructure represent
unique scenarios in which design, inspection, and construction functions cannot
easily be separated (Kagan et al., 1986).
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134 UNDERGROUND ENGINEERING FOR SUSTAINABLE URBAN DEVELOPMENT
Operation Phase Lifecycle Economic Benefits and Costs
As noted earlier, cost benefits accrued from operation of any infrastructure
system are difficult to quantify. Benefits may include enhancements to quality of
life, reductions in travel and travel time, and increases in productivity. There are,
however, inherent benefits related to the operation of underground infrastructure.
Johnson (2006) found that the conversion of unsightly overhead electrical lines
to underground lines resulted in increased property values and improved aesthet-
ics within neighborhoods. Other lifecycle societal economic benefits include
reduced outages, transmission losses, and greenhouse gases; reduced network
maintenance costs; fewer electrocutions; and fewer motor vehicle collisions with
poles (IFC Consulting, 2003). The average cost of burying existing electrical
lines is estimated to be $1 million per mile, which is almost 5 to 6 times (Parsons
Brinkerhoff, 2012) or 10 times (Johnson, 2006) the cost of a new overhead line.
However, the maintenance and operating costs of underground electrical lines
have been reported to be about one-tenth of those of aboveground lines because
of reduced transmission losses over the life cycle (IFC Consulting, 2003). In
addition, underground cables also may enable increases in power transmission
capacity (Al-khalidi and Kalam, 2006).
Chapter 4 describes security issues associated with underground infrastruc-
ture but shows that there are inherent security benefits to putting infrastruc-
ture underground. Underground systems have a lower risk of disaster failure to
earthquakes, hurricanes, tornados, tropical storms, heavy snow events, monsoon
winds, and natural disasters, but these systems may be vulnerable to flooding.
These lower risks could translate into reduced insurance premiums over the life
cycle of the asset (e.g., De Saventhem, 1977).
Renovation and Replacement Phase Lifecycle Economic Benefits and Costs
Renovation of infrastructure (i.e., asset preservation) often improves opera-
tion at a fraction of the cost of full replacement. Consequently, renovation meth-
ods such as lining or grouting of pipelines and external face-lifting of buildings
are preferred when existing infrastructure is still structurally acceptable but
requires renewal to a “like new” condition. Replacement may be deemed neces-
sary because of obsolescence, inflexible design, or irreparability of the exist-
ing infrastructure. Surface infrastructure can be replaced with relative ease as
compared to underground infrastructure; however, the frequency of the need for
repairs and renovations may be less for underground infrastructure because of
the protection the underground provides. On the other hand, if underground infra-
structure becomes obsolete—for example, the largely abandoned underground
freight tunnel system beneath downtown Chicago (see Box 3.7)—it may be dif-
ficult to repurpose the space for another use.
Careful planning of underground use for well into the future can minimize
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LIFECYCLE SUSTAINABILITY, COSTS, AND BENEFITS 135
the rate at which infrastructure becomes obsolete. Utilidors (described in Chapter
3), for example, provide flexibility to switch out or add utilities when dictated
by obsolescence, deterioration, or capacity issues. Utilidors streamline utility
easements and provide improved accuracy in locating existing buried utilities,
which is advantageous for line maintenance and replacement. Canto-Perello
and others (2009) found that utilidors minimize the potential dilemma of mutual
interference between utilities and transportation networks. Additionally, placing
utilities in utilidors results in minimizing physical damage to surface streets from
continual cutting of pavement when installing, inspecting, maintaining, repairing,
or replacing lines.
LIFECYCLE ENVIRONMENTAL BENEFITS AND COSTS
Since 1970, the National Environmental Protection Act (NEPA) has required
“federal agencies to integrate environmental values into their decision making
processes by considering the environmental impacts of their proposed actions
and reasonable alternatives to those actions” (EPA, 2010). As a result, environ-
mental impact statements and analyses have been completed for a wide range of
underground developments. However, these impact statements are prospective
in nature to inform planning decisions, rather than retrospective assessments of
actual environmental impacts from projects as built. For example, whereas many
earlier environmental impact analyses did not include greenhouse gas emission
effects, recent environmental impact statements address findings such as the 2009
finding by the EPA Administrator that greenhouse gas emissions (carbon dioxide,
methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexa-
fluoride) threaten public health and the welfare of current and future generations
as a result of climate change effects (EPA, 2009). Finally, environmental impact
statements typically do not include the supply chain or indirect environmental
impacts in the analyses and therefore do not provide a complete lifecycle assess-
ment. For estimating carbon footprint or greenhouse gas emissions, these indirect
emissions are termed Tier 3 emissions and often are significant for the provision
of goods and services (Matthews et al., 2008). In particular, the production of
cement used in underground construction generally results in significant green-
house gas emissions.
Construction methods play a major role in greenhouse gas emissions.
Sihabuddin and Ariaratnam (2009) compared airborne emissions from trenchless
versus open-cut pipe replacement on the same project and found that trenchless
reduced pollution on the order of 80 percent. Few studies have looked at the
effect of underground infrastructure over its entire life cycle or have compared
lifecycle assessments of overhead and underground infrastructure delivering the
same service (see Box 5.1).
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136 UNDERGROUND ENGINEERING FOR SUSTAINABLE URBAN DEVELOPMENT
BOX 5.1
Environmental Lifecycle Comparison of Overhead and
Underground Power Distribution
Bumby et al. (2010) compared buried and overhead power distribution
using Southern California Edison designs for medium voltage cables using a
process-based lifecycle assessment per guidelines from the International Or-
ganization for Standardization.a The Figure shows the various process steps
involved in the life cycle for the underground power distribution assembly.
Their assessment indicates that overhead distribution assemblies as designed
by Southern California Edison have lower overall emissions. The values are
heavily influenced by the additional material inputs required for cable manu-
facturing of the underground distribution assembly. Secondary factors include
the shorter estimated life for underground cables due to underground heating
effects and lost carbon sequestration due to timber production because carbon
is captured in the growth of trees. The study also estimated eco-indicator im-
pacts common in Europe (see Guinée, 2002, for standards), including abiotic
depletion potential, acidification potential, eutrophication potential, freshwater
aquatic ecotoxicity, human toxicity potential, photochemical ozone creation
potential, and terrestrial ecotoxicity potential. For reasons similar to those for
greenhouse gas emissions, the overhead design had lower environmental
impacts in these categories.
The study omitted some categories that require further research. The
underground cable had lower resistance, so transmission power losses may
be lower underground. The study does not consider land use impacts and
the net urban system energy usage or environmental effects given either
overhead or underground use. The construction material advantage for power
cables may not exist for overhead structures used for other purposes such as
carrying vehicles. Moreover, siting overhead power transmission lines often
can be difficult for aesthetic reasons. This study demonstrates the difficulty of
obtaining comprehensive but rigorous results from triple bottom line analyses.
Such analyses can include only the issues for which data are available and
are unable to address broader performance, resilience, societal, or environ-
mental issues.
SOCIAL BENEFITS AND COSTS
This section summarizes some of the social benefit and costs associated with
the use of underground space and discusses what additional data or changes in
assessment practices might be helpful to making sound investment and opera-
tional decisions.
As described in earlier sections, the framework for the economic and envi-
ronmental lifecycle assessment of project alternatives is reasonably well under-
stood—including how to manage conceptually the combination of quantitative
and subjective comparisons. One challenge to lifecycle cost analysis is that some
of the strongest advantages of underground structures tend to be more long term
and qualitative (including benefits to quality of life or urban resilience), while
disadvantages tend to be more readily identifiable and quantifiable (e.g., startup
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LIFECYCLE SUSTAINABILITY, COSTS, AND BENEFITS 137
FIGURE Process flow diagram for the underground power distribution assembly. Colors
indicate data source as commercial lifecycle assessment databases (pink), Southern Califor-
nia Edison (orange), or a mix of these two sources (yellow). SOURCE: Bumby et al., 2010.
Reprinted with permission from American Chemical Society.
aISO 14044 specifies requirements and provides guidelines for lifecycle assessment in-
cluding scope, inventory analysis phase, impact assessment phase, interpretation phase
(ISO, 2006).
costs). Another challenge is that few individuals are expected to state a preference
for being in an underground facility rather than a surface facility for extended
periods. In many cases, the benefits come from what the underground facility
permits in terms of an improved surface environment, mobility, or services rather
than from the superior attributes of the facility itself.
Underground space use, if well planned, permits excellent options for urban
transportation and provision of utility services, along with a range of other desired
facilities, all with low-impact on the surface environment, heritage, and, poten-
tially, ecology. In other words, well-planned underground construction supports a
compact, well-functioning, livable, and sustainable urban environment. The pro-
tection and resilience of an underground structure may benefit the project owner,
but if it affects the ability of society to function effectively, for example, after a
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138 UNDERGROUND ENGINEERING FOR SUSTAINABLE URBAN DEVELOPMENT
disaster, then it has a much broader societal impact. Likewise, communities are
increasingly resisting construction-caused disruption from new infrastructure
projects. The project owner may pay some costs attributable to the disruption—
such as business loss—but the owner does not pay for traffic delay costs and the
diminished livability of the neighborhood due to construction noise, vibration,
dust, and diminished air quality. Capturing all of the appropriate costs when com-
paring project alternatives remains a challenge and a topic for future research.
Multiple papers identify issues to be considered with respect to utility proj-
ects (e.g., Gilchrist and Allouche, 2005) and provide case examples of the appli-
cation of social and indirect costs to project decision making (e.g., Li et al., 2009).
However, typically only a few of the key social or indirect costs are considered
because of a lack of impacts data or a lack of accepted costing for disturbances
effects. Papers that describe analyses of a variety of costs (e.g., Pucker et al.,
2006) typically find that traffic delay costs are the most important social cost in
urban areas and can rival or exceed the cost of the construction itself for some
street utility work. In suburban or rural areas, traffic delays are typically less
severe except on key arterial routes.
Local opposition to a project typically is based on the social and indirect
costs expected as a result of project construction and operation. Often, these costs
can be mitigated through less disruptive construction methods (e.g., trenchless
technologies for utility construction and repair, and bored tunnels instead of cut-
and-cover tunnels for road and rail projects) and restrictions or modifications
to working practices (e.g., limits on working hours, noise, and vibration). As
restricted working practices are adopted to accommodate neighborhood opposi-
tion, unpaid social costs become hard construction costs and potentially increase
construction risks. Least disruptive construction methods are more likely chosen,
avoiding the need to calculate social costs.
Another issue worth noting is that construction and operation impacts of
major infrastructure projects represent a moving target in terms of acceptable
compromises for limiting impacts on neighborhoods. Discussions about trans-
forming a surface or elevated transportation project to an underground alignment,
or transforming from cut-and-cover to bored tunnel construction, typically con-
sider noise and air quality impacts at the tunnel portal. In general terms, the shift
underground maintains mobility for many people in the urban area and lessens
the environmental impact on most of the area through which it passes. However,
construction vibrations (e.g., from blasting) and noise and air quality emissions
become more localized—making them more bothersome to those in the immedi-
ate vicinity, but also more controllable. The drawback is that the increasingly
high standards to which underground projects may be held increases their costs
relative to surface or elevated alternatives. Critical decisions regarding major
infrastructure initiatives for urban areas ride on such concerns. The ability to
adequately compare radically different infrastructure alternatives (including the
“do nothing” alternative) that potentially change the face of the city for better or
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LIFECYCLE SUSTAINABILITY, COSTS, AND BENEFITS 139
worse remains a daunting challenge. In many cases, a strong political decision is
finally made in the face of widely different opinions and conflicting cost-benefit
analyses.
Accommodating social and human factors issues and improving underground
designs are not just window dressing essentially technical projects. How these
issues are addressed in the project’s design and construction can have profound
effects on its cost, acceptance by the public, and impact over its life cycle. There is
no single best answer, but it is important to understand the various ramifications.
The Stockholm (Sweden) Metro has individualized station designs decorated by
artists to make distinctly different environments in each station (Winqvist and
Mellgren, 1988). Washington, DC, Metro stations have a similar look that cre-
ates familiarity for ease of use. Large station caverns often are used to create an
impressive public space underground, but at a cost in terms of initial construction
and probably in operation as well (as pointed out by O’Rourke, 1983). Allowing
variety in design approaches based on a better understanding of how to create
interesting and enjoyable underground spaces without large increases in cost or
space requirements remains a challenge, as does quantifying the social costs and
benefits over the life cycle of the infrastructure.
RESEARCH NEEDS FOR LIFECYCLE COSTS AND BENEFITS
As discussed earlier, many factors are incorporated into full lifecycle cost
analysis. Consideration of those factors may shift the perception of the feasibil-
ity of underground space use—from that of expensive and risky, to wise and
most cost-effective in the long term. Largely needed is a better understanding of
what aspects of project planning, design, construction, and operation contribute
the most to project costs and long-term benefits and performance. The goals of
lifecycle cost analysis are to reduce costs where possible through technology
enhancements and design and administrative changes, as well as to better articu-
late the long-term benefits to the urban area—in monetary terms if possible—but,
at least through well-documented examples of the positive and negative impacts
of underground projects.
Considering the high profile of many underground road and rail projects, it
is surprising that comprehensive documentation is hard to find. Planning stud-
ies are available, but they lack the retrospective assessment of actual costs and
benefits. There is anecdotal or partial evidence of the positive environmental
and financial impacts of replacing aboveground transportation structures with
underground alignments on neighborhoods worldwide. For example, the Boston
Globe reported in 2004 (Palmer, 2004):
According to an in-depth review of the City of Boston tax assessing
records by the Globe, in the 15 years since the Central Artery tunnel
project began, the value of commercial properties along the mile-long
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140 UNDERGROUND ENGINEERING FOR SUSTAINABLE URBAN DEVELOPMENT
strip that this year will become the Rose Kennedy Greenway increased
to $2.3 billion, up 79 percent. That’s almost double the citywide 41
percent increase in assessed commercial property values in the same
period.
When adjusted and aggregated over the entire Central Artery alignment,
the increase in land values could be of the same order of magnitude as the cost
of such a difficult and expensive project. What appears to be lacking in this and
other examples is careful and defensible study of the financial and environment
changes over, say, a decade following project completion. Retrospective, com-
parative studies of the costs and impacts of the various types of underground
construction projects are needed. To be useful, these studies must be conducted
in a comprehensive and scientific manner and must consider economic, environ-
mental, and social impacts.
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