time losses of the other road users. In Mayeres (1993) it was shown that the effect of the
marginal change in speed on the operating costs and on air pollution costs is of relatively
minor importance; therefore, we have decided not to include them. In our calculation,
congestion is assumed not to influence the demand of the other road users. We are,
therefore, dealing with short run marginal congestion costs. Their magnitude varies
according to the transport equilibrium considered.