Access pricing, infrastructure investment and intermodal competition

•We study the conditions for investing in a complementary or rival infrastructure.•This paper provides a methodology to be considered in cost–benefit analysis.•Optimal access prices for each infrastructure cannot be set independently.•The investment is socially desirable if there is an increase in social welfare.•Key parameters are the number of users and investment costs.

This paper considers the existence of a given transport infrastructure and analyzes the optimal conditions for investing in a complementary or rival new infrastructure. The model allows us to identify some key variables to be considered in cost–benefit analysis and highlights the importance of socially optimal access pricing in relation to investment decisions. The socially optimal conditions for investment depend on, among others, the cross-effects between different modes of transport, the volume of demand, the construction cost of the new infrastructure, and the restrictions faced by the regulator.