The construction of a new railway infrastructure requires an enormous resource mobilisation, has a very long useful life and the possible alternative uses of the investment made are few. Consequently, any investment of this kind needs to always be preceded by a detailed analysis in order to ensure the best possible result.

The purpose of this thesis is to set out a methodology capable of determining the combination of maximum speeds of a high-speed railway line that makes it possible to obtain the maximum returns with the minimum costs. This doctoral thesis develops and defines a methodology capable of determining the combination of maximum speeds that obtains the best results in socio-economic terms (greater socio-economic NPV) subject to the established restrictions (limitation of financial profitability and investment cost).