The gap between socio-economic and financial profitability is a major barrier in the development of the trans-European network. When a project is not sufficiently profitable for the private sector, direct government contributions or introduction of user charges can be used to let the private sector participate. However, even when a project offers a sufficient financial return for the private investor, there may be arguments for public intervention. The public sector could be involved to safeguard the interests of non-users, to improve risk sharing, or to mix public and private skills, for example combining the public sector experience of infrastructure planning with the commercial and financial skills of the private sector.