Environmental Effects of Public Transport: On the Gap between Average and Marginal Costs

Given the difference between peak and off-peak occupancy rates in public transport, the average emission pertraveller kilometre is lower in the peak than during the off-peak period. For cars a reverse pattern can be observed. However, in this paper it is argued that it is much more fruitful to analyse environmental effects in marginal than in average terms. This calls for a careful analysis of capacity management policies of public transport suppliers that are facing increases in demand both during the peak and off-peak period. A detailed analysis of capacity management of the Netherlands Railways reveals that the off-peak capacity supply is mainly dictated by the demand levels during the peak period. Issues that receive attention in the analysis are the effects of frequency increases and size of vehicle increases on environmental effects. Also environmental economies of vehicle size are taken into account in the analysis. The main conclusion is that the marginal environmental burden during the peak is much higher than is usually thought, whereas it is almost zero at the off-peak period. Thus, one arrives at a pattern that is entirely reversed compared with the average environmental burden. The conclusion is that policies based on average environmental performances would lead to misleading conclusions.