This thesis shows the advantages of simple models for analysis of railway operation. It presents two tools for infrastructure and timetable planning. It shows how the infrastructure can be analysed through fictive line designs, how the timetable can be treated as a variable and how delays can be used as performance measures. The thesis also gives examples of analyses of complex traffic situations through simulation experiments. Infrastructure configuration, timetable design and delays play important roles in the competitiveness of railway transportation. This is especially true on single-track lines where the run times and other timetable related parameters are severely restricted by crossings (train meetings). The first half of this thesis focuses on the crossing time, i.e. the time loss that occurs in crossing situations. A simplified analytical model, SAMFOST, has been developed to calculate the crossing time as a function of infrastructure configuration, vehicle properties, timetable and delays for two crossing trains. Three measures of timetable flexibility are proposed and they can be used to evaluate how infrastructure configuration, vehicle properties, punctuality etc affect possibilities to alter the timetable. Double-track lines operated with mixed traffic show properties similar to those of single-tracks. In this case overtakings imply scheduled delays as well as risk of delay propagation. Two different methods are applied for analysis of double-tracks: a combinatorial, mathematical model (TVEM) and simulation experiments. TVEM, Timetable Variant Evaluation Model, is a generic model that systematically generates and evaluates timetable variants. This method is especially useful for mixed traffic operation where the impact of the timetable is considerable. TVEM may also be used for evaluation of different infrastructure designs. Analyses performed in TVEM show that the impact on capacity from the infrastructure increases with speed differences and frequency of service for the passenger trains, whereas the impact of the timetable is strongest when the speed differences are low and/or the frequency of passenger services is low. Simulation experiments were performed to take delays and perturbations into account. A simulation model was set up in the micro simulation tool RailSys and calibrated against real operational data. The calibrated model was used for multi-factor analysis through experiments where infrastructure, timetable and perturbation factors were varied according to an experimental design and evaluated through response surface methods. The additional delay was used as response variable. Timetable factors, such as frequency of high-speed services and freight train speed, turned out to be of great importance for the additional delay, whereas some of the perturbation factors, i.e. entry delays, only showed a minor impact. The infrastructure factor, distance between overtaking stations, showed complex relationships with several interactions, principally with timetable factors. / QC20100622 / Framtida infrastruktur och kvalitet i tågföring