The main objectives of investment on railway are improving connectivity and access to services; generate employment and amenities; while delivering cuts in carbon emissions, reductions in traffic noise, pollution and congestion. Within that general context, the existing options to improve a railway line are the upgrading of the existing line, which is called the brown field option, or to build a brand new line in the corridor, which is called the green field option and which is assumed a state of art line, i.e. a High Speed Line. There is, nevertheless, a third option that could be followed in which, first the existing line is upgraded and then a new High Speed Line is built in the same corridor. This latter option is acknowledged as economically inefficient, but it is needed to find out to what extend that assertion is true. The purpose of this study is, then, to reach a conclusion on that statement through the analyses of actual cases, i.e. not through a theoretical exercise but through an empirical research. In the first stage of the research two corridors that met the requirements of the study were identified: the Madrid - Valencia Line in Spain and Bordeaux – Spain Line in France. From the analysis of those corridors it was learnt that, indeed, building a new High Speed Line after upgrading the existing line in that corridor will not be economically efficient unless the new line is built after a number of years. That delay could be around 10 years, and will depend on the level of investment carried out for the upgrading and the expected growth of transport demand in the corridor.DOI: http://dx.doi.org/10.4995/CIT2016.2016.4081