C R Brems, N B Kristensen, COWI;
When considering infrastructure tolling the White Paper on European Transport Policy states, that tolls should reflect the costs that the road user pose on society. An important part of these costs origin from congestion. This paper presents a newly developed method to evaluate the congestion costs based on both delays and increased uncertainty in travel time. The congestion costs are quantified for three different road types: Urban road, arterial road and motorway.
The effects of congestion on travel time are described by distributions of travel time based on observations of traffic intensities and travel times. Distributions are gathered for each of the three different road types. As expected it was found that at low volume/capacity ratios the traveller has a lowtravel time with little expected variation, whereas at higher volume/capacity ratios the travel time does not only increase, the expected variation in travel time increases as well.
With these observed distributions of travel time an optimal planned travel time is derived based on the differences in the traveller's valuation of travel time, early arrival and late arrival. If a traveller has a fixed arrival time and therefore values late arrival three times as high as travel time or early arrival, it is proven by the new method that the optimal planned travel time is the 75%-fractile of the travel time distribution. In this way the travel time can be split in free flow travel time, expected delay, and unexpected delay and the time components can be evaluated accordingly.
Furthermore, the distributions are used to derive marginal costs of congestion including effects of both delays and increased uncertainty in travel time. The marginal costs vary with traffic intensity and thereby by time of day. The preliminary results show no significant marginal costs for traffic intensities below capacity and fast increasing marginal costs when traffic capacity is reached. This corresponds to the theoretical findings regarding marginal costs. For motorways the preliminary results indicate that the marginal costs of congestion in the peak hour amounts to 0.25 Euro/vehkm, while the corresponding figures for urban and arterial roads varies from 0.5-1.1 Euro/vehkm.
Association for European Transport