Decision-making model for track system of high-speed rail lines : Ballasted track, ballastless track or both?

Abstract: During the 50 years of existence of high speed railways, the track structure solutions have developed both in number and in type. As of today, in case of conventional railway, there are 2 main types one could mention: ballasted and ballastless track solutions. However, there is no standardized procedure for choosing between these systems and between their respective variants, the decision is made on a case-by-case basis. This thesis aims to create a generic framework for decision making, primarily taking into account technical details. The model, the input parameters and variables can be easily adjusted and customized based on national standards, practices or other considerations, but the primary focus in the thesis have been the current Swedish regulations. The thesis has an overview on the influencing factors and attempts to include the most crucial ones of these into a decision-making model. This model compares 3 alternatives, namely the ballastless alternative, the ballasted alternative and the alternating system option, in which case the track system selection happens based on local factors, such as geotechnical conditions. These are considered and evaluated through Fuzzy logic, which supports the system selection affected by various sources of uncertainty. The decision is finally made through an LCC calculation. In order to handle the great uncertainties in the data used in the LCC, a Monte Carlo simulation is performed. The main added value of the thesis is considered to be the methodology for choosing the systems based on life-cycle cost after careful technical evaluation. This approach might provide basis for decision for track systems of high speed rail lines.