Environmental Engineering Reference
In-Depth Information
to ensure that its consequences are offset with
a minimal budget. This will hold particularly
true in the forthcoming decades as even stronger
accountability will be required by airports in
their management of environmental issues. For
instance, it is common practice for airports to
mitigate the noise due to aircraft operations with
programs that improve the acoustic insulation of
neighboring residential areas; airports have also
recently participated in efforts to become carbon
neutral by purchasing carbon offsets (ACI, 2009a).
While the cost of offsetting such impacts will be
subject to debate, we maintain that it is easier and
more objective to score environmental criteria in
this manner than using preferences defined by the
subjectivity of individual experts. Specific impact
levels are hard to determine as some effects occur
at a global level. Therefore, weighting impacts ac-
cording to their mitigation costs seems adequate.
The use of a monetary evaluation simultaneously
solves the problem of incommensurable units
and allows a simple aggregation of scores using
a linear additive function.
The cost function is used to produce criteria
weights that reflect the mitigation cost of a par-
ticular environmental effect. The actual perfor-
mance of the criterion is kept and multiplied by
the weight. Let
A
= {
A
i
, for i = 1,2,…,n} be the
finite set of alternatives that are evaluated. We
consider a set of criteria that are quantitative and
for which mitigation costs are assessed. Let
C
=
{
C
j
, for j = 1,2,…,m} be this finite set of criteria.
At the scoring step, each criterion
C
j
is assigned
a score
S
ij
for each alternative
i
. These scores are
expressed in the particular units of each crite-
rion, preventing aggregation. To overcome this
issue, we introduce a mitigation cost function
c
that computes a weight
W
j
for each score
S
ij
. The
score is initially expressed in the unit specific to
each indicator. The score is then multiplied by a
weight expressed in currency per indicator unit.
The resulting product is expressed in currency
for all the concerned criteria, allowing their ag-
This weight
W
j
represents the cost for mitigating
the impact caused by one single unit of the score
S
ij
. The aggregated score of all cost-based criteria
is
CP
i
, the cost performance of alternative
i
and
it is given by:
j
∑
1
CP
=
S W
⋅
i
ij
j
j
=
The methodology for estimating the costs of
environmental impacts caused by airport devel-
opment is often the subject of vibrant debate and
little research on the topic has been produced
as yet. The methodology proposed here defines
mitigation cost as the monetary amount paid by
airport developers and authorities for the purpose
of offsetting direct environmental impacts of
their development activity. There are, however,
arguments for considering the costs incurred by
indirect impacts on a much larger scale, such
as long-term health and social consequences to
society. We choose to restrict the methodology to
the first definition for two reasons. First, there is
little understanding of, and evaluation procedures
for, the financial burden of indirect impacts. For
instance, there is as yet no consensus as to the
consequences of global warming or heat islands.
Second, our goal in developing this method is
to encourage airport planners and designers to
achieve greener airport design. Using direct miti-
gation costs directly influences the budget of the
project and thus creates an inherent incentive for
decision makers to limit mitigation needs as this
also minimizes expenses. The strategy of first
avoiding, then minimizing, and finally mitigat-
ing impacts only if they could not be avoided
or minimized, ensures that mitigation is the last
resort. Although airport authorities do have the
social responsibility to address the consequences
of their activity to society in general, we believe
it is premature to include such social costs in the
method as the computation of accurate metrics is
currently not possible.
