Political trends as well as general growth of the transport market set new challenges to railways and particularly to rail infrastructure managers. Rail infrastructure must become more efficient, which is to say that costs must be reduced and the use of capacity optimised, through better timetabling and network adjustments. But above all, rail infrastructure management should tackle strategic issues (on the long-term), hence the need for more adequate planning tools. Nowadays, infrastructure managers tend often to concentrate on operational and short-term problems ; meanwhile, reshaping rail networks requires several years of planning and implementation. In this context , the paper presents a methodology and the bases for the development of an effective decision support system to help infrastructure managers in setting up development strategies for rail corridors or networks. The methodology deals not only with the planning of investments in capacity (timetabling and timetable analyses), but takes also into account the impacts of timetable on the maintenance and renewal policies, in particular through the analysis of interactions between service deteriorations and track possessions. The methodology covers both the analysis of the availability and the reliability of capacity, and the maintainability of the infrastructure as well. The paper shows the importance of the long term planning of rail infrastructures and proposes a way of tackling both the analysis of capacity investments and the elaboration of maintenance and renewal policies. The presented approach is based on two existing software, CAPRES and FASTA, and on a third model, MRPOL, currently under development.