In order to calculate the marginal

In order to calculate the marginal external noise costs, one needs to determine the
effect on the noise level of an additional car km. The index for noise used is the energy
mean sound level, L,,(dB(A)). It gives the average sound level over a given period. The
Institut Bruxellois pour la Gestion de 1’Environnement (1995) presents a number of func-
tions that relate the noise level in a street to, inter alia, the traffic flow. We assume that
the average street in Brussels has a U-shape, i.e. that it has houses on both sides of the
street. In that case, the function is: