Damage refers to human health, material damage and effects on plant life. These have been
separated out in a number of studies. They are summarised in Kågeson (1992a), from which most of the
information in Table 2.7 is drawn. It should be noted that, as for noise, the estimates based on willingness to
pay are generally much higher than those based on damage. For example, the Planco study indicates
pollution costs higher by a factor of 1.5 to 2.
Apart from the UPI estimate, which is very high, the percentages obtained are relatively little
dispersed around a mean value of the order of 0.4 per cent of GNP. The breakdowns by mode and by traffic
unit can be examined either in terms of physical or monetary quantities. In terms of physical quantities, the
following studies have been done: