IEEE Systems, Man and Cybernetics Magazine - July 2019 - 13

and on digital connectivity being essential for all infrastructure networks to function. These are not the only interdependencies, but they are the most ubiquitous and are becoming
reinforced by the overarching directions of technological
change, i.e., toward electrification (in part motivated by the
desire to decarbonize the power sector) and digitization.
Other significant forms of interconnectedness include the
reliance of most thermoelectric power plants on water for
cooling and the dependence of practically all infrastructure
upon transport networks (mostly roads) to convey workers
to infrastructure sites, even during catastrophic events.
Interdependencies also bring opportunities-for example, by using the batteries in electric vehicles to store electricity from renewable energy supplies and then deploying
the stored energy to better match electricity demand with
supply. Risks of water shortage in many parts of the world
mean there are increasing efforts, led by countries like Singapore and Israel, to close the urban water cycle by directly reusing wastewater in sewage for urban and agricultural
water supplies. There is also growing interest in the ways
in which green infrastructure (like green spaces and wetlands in urban areas) can substitute for gray infrastructure, often by providing multiple services like sustainable
urban drainage, purification of wastewater, and urbanarea cooling (through shade and transpiration).
These interdependencies influence everyday planning
for infrastructure investment and operation and they affect
infrastructure performance during extreme events. One set
of crucial imponderables for energy system planners is how
many electric vehicles there will be in the future, when and
where they might need to be charged, and whether they can
be used as battery storage devices at times of excess
renewable energy supply. Another group of questions
relates to the growing need for digital infrastructure to service transport technologies like autonomous vehicles. Planning one infrastructure network in isolation will overlook
these crucial interdependencies. The framework set out
next is designed to explicitly and conveniently incorporate
a quantified understanding of interrelationships in a system-of-systems methodology.
A Framework for Infrastructure
System-of-Systems Analysis
The ITRC is a group of seven of the United Kingdom's leading universities that has been working since 2011 to develop, test, demonstrate, and deliver methodology for
national infrastructure assessment. It was backed by
GB£4.7 million of funding from the United Kingdom's Engineering and Physical Sciences Research Council and in
2015 was awarded an additional GB£5.3 million to continue the research program to 2020. The ITRC has adopted a
system-of-systems approach to infrastructure, promoting
cutting-edge research on the interdependencies among the
following infrastructure sectors: energy (electricity and
gas), transport (road, rail, ports, and airports), digital communication (fixed, mobile, and satellite), water (supply,

wastewater treatment, drainage, and flood protection),
and solid waste. The assessment methodology is depicted
in Figure 1.
◆ Scenarios: The system-of-systems framework shown in
Figure 1 uses scenarios (top left box) to explore uncertainty in a number of possible futures, i.e., in terms of
the global and national economy, population/demography at the national and local scale, climate change, and
technological development. By examining a wide array
of possible scenarios, we can test the sensitivity of various infrastructure policies and plans to different possible future states of the world. These scenarios explore
the possible range of contextual factors that are largely
outside the control of decision makers responsible for
national infrastructure. Of course, there is feedback
between the infrastructure system and these factors,
notable in terms of regional economic development. For
example, the provision of infrastructure can stimulate
the economy, providing new employment opportunities
and hence changing where people live. Such feedback is
important to recognize but is much more difficult to
quantify [19]; attempting to model it would introduce
additional complexity that for the time being we consider to be unwarranted. Nonetheless, for the sake of simplicity, it is preferable to explore the possible impacts of
infrastructure investment on regional economies by
using scenarios that test the possibility of additional
growth being stimulated by infrastructure provision.
◆ Strategies: Alongside scenarios, our framework
explores one or more infrastructure strategies. Strategies are sequences of infrastructure investments and
policy/regulatory interventions that are intended to
modify demand for or provision of infrastructure services. Strategies must be sufficiently adaptable to cope
with uncertain scenarios-for example, those involving population growth. On the other hand, a national
infrastructure strategy must give a clear sense of
direction about what policies and investments need to
be implemented as well as where and when. The balance between supply-side and demand-side intervention depends on the circumstances and the availability
of technologies. Overprovision of new infrastructure
(supply side) can result in infrastructure being underutilized or resources being used inefficiently. This has
stimulated increasing interest in demand-side instruments like pricing (e.g., congestion charging) or regulation to mandate efficiency standards (e.g., for electric
appliances). However, these are not cost free and can
require strong political commitment in the face of
resistance by infrastructure users.
◆ Models and metrics: Scenarios and strategies provide
the boundary conditions for the coupled-system modeling depicted in the center of the diagram in Figure 1.
NISMOD runs in a simulation mode, i.e., for a given set
of input conditions (scenarios and strategies), the coupled-system models simulate system performance and
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IEEE Systems, Man and Cybernetics Magazine - July 2019

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