The White Paper (European Transport Policy for 2010, 2001) recognises the importance of establishing an efficient pricing system in any transport infrastructure. In other words, prices should be equal to the corresponding social marginal costs and, consequently, it is necessary to have a variable pricing structure depending on the type of vehicle, the infrastructure and the time period in which traffic is analysed. The main objective of our paper is the identification and estimation of the principal components of this optimal price in Spanish interurban road transport. Using data for the year 2000, our paper estimates the optimal prices according to vehicle type and compares these results with the prices estimated from the current road tax system.

Key words: prices, interurban transport, externalities, social marginal cost, congestion.
JEL classification: H23, R41, R48.