The visible effects are the easiest to predict; the use of photo-montage and mock-ups can give an
excellent idea of how the future infrastructure will appear and fit into the landscape. Of course the evaluation
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Internalising the Social Costs of Transport - Chapter 2
of the specific result will still be highly subjective. As regards noise and local pollution, the evaluation can
be less subjective, but knowledge of the effects of environmental impacts is generally more difficult to
obtain. Many impact studies merely list the number of people who will be affected (for example, those living
within a certain distance from the infrastructure). This approach does perhaps provide a satisfactory image of
the effects of the pollution moving through the space surrounding the infrastructure; however it is used
primarily for noise, where the propagation of the noise is highly sensitive to the local geometry, and it is only
through investigations at the construction stage that greater precision can be introduced and adequate
measurements considered. This very often leads (in cities, at least) to infrastructures being placed
underground, for reasons of noise and appearance, much more for than reasons of local pollution. One
wonders whether this situation can be improved and the effects of noise integrated in some more precise
manner. To do this, one would have to be capable of improving the prediction of the effects, which could
involve significantly improving the modelling capacity in these fields.