Railway transportation has great potential, but interdependencies in the railway traffic make trains very sensitive to disturbances, which can bedifficult to handle. Using railway in an intermodal transport chain may complicate the interconnections with other modes if there is large uncertainty in the performance of the railway. A study based on interviews with several customers of the Swedish National Railway Administration shows that the customers lack information regarding occurrences of disturbances and the consequences for their trains, i.e. the new estimated time of arrival. This information is necessary when taking actions within the customers’ organisation to minimise the negative impacts. Predicting the consequences of a disturbance and the effects of counter measures taken by the Swedish train traffic managers is today an overwhelming task considering there is no computational decision support available. However, provided that the traffic and decision-making could be simulated, the effects from disturbances and actions taken could be computed. Requirements regarding computational time for a simulation are obviously significant and affect the usefulness in a real-time environment. For strategic purposes, a simulator could also serve as an analytical tool for evaluating strategies for handling certain types of disturbances. An approach to model the different layers of such a simulator, taken into account the infrastructure, the traffic flow and the influence of the traffic management decisions and transport operators, is presented. The part that covers the interaction between train traffic and infrastructure has been implemented as a small-scale discrete-event simulator. The simulator is extended by an optimisation approach, attempting to act as decision support for the train traffic managers when handling disturbances by generating effective counter measures. It is composed by a linear model specifying the timetable of a sub-network and solved by optimisation software. Iteratively, a heuristic is applied to modify the timetable by changing meets and overtakes and generate a new updated linear model to be solved. In addition to consider the train traffic system as an explicit part of a transport chain, it can be seen as a black box where some relations between input and output are known. We have investigated how uncertainty in the reliability related to one or several transport links can be handled when combining several links into a transport chain. A simulation-based approach is proposed.

Railway scheduling problems are quite popular scheduling and optimization problems which are treated in a large variety of papers and projects. Many special and even quite general situations have been investigated theoretically and also a variety of applied approaches tested on real-world instances has been developed.This thesis mainly deals with the problem of scheduling trains in railway networks with respect to given routings, fixed minimal travelling times, and other constraints like time-windows. It combines the theory of some well-known scheduling models with its applications in railway scheduling. The railway scheduling problems considered in this work are closely related to job-shop scheduling problems with blocking and some additional constraints. Therefore part of this research is related to these shop scheduling problems. Theoretical scheduling models are extended, complexity results are derived and solution methods are proposed. Most results are applied to the considered railway scheduling problems. In addition to approaches which treat railway problems as a whole also decomposition methods for these problems and corresponding solution methods are presented. These solution methods are tested and compared with simple greedy procedures.

Rail transport plays a key role in the mobility of passengers and goods. It is expected to grow the decarbonization of society. In that context, it is important to use the railway network efficiently, and jointly planning trains and network maintenance allows for better use of resources. This master thesis focuses on the integration of regular maintenance slots in a timetable while minimizing the impact on rail traffic and maintenance costs. The problem has been modeled as a mixed-integer linear programming formulation. First, we study the modeling of the interactions between trains, and we focus on the possible conflicts due to maintenance slots. Two approaches are compared: an aggregated one and a detailed one close to maintenance slots. We analyze the computation time and the quality of the solution on a real-life timetable with different maintenance scenarios. The results show while the aggregated approach is useful for finding reasonable slots, the detailed one is necessary to achieve high quality solutions with minimal traffic impact. In the second step, we reduce the computation time by using construction heuristics. We use a greedy algorithm to find realistic maintenance slots combined with a train-fixing heuristic. Our experiments have shown that theses heuristics reduces significantly the computation time (with more than 50% on the considered test instances) for solutions of equivalent quality. Limitations of the model and improvements are discussed. / Järnvägstransporter spelar en nyckelroll för passagerar- och godstransporter. Den väntas öka koldioxidminskningen i samhället. I det sammanhanget är det viktigt att använda järnvägsnätet effektivt och en gemensam planering av tåg och underhåll av nätet gör det möjligt att utnyttja resurserna bättre. Den här masteruppsatsen fokuserar på integrering av regelbundna underhållsfönster i en tidtabell samtidigt som man minimerar effekterna på järnvägstrafiken och underhållskostnaderna. Problemet har modellerats som ett linjärt optimeringsproblem med blandade heltal. Först studerar vi hur interaktioner mellan tåg kan modelleras med fokus på konflikter som uppstår vid underhållsfönster. Två tillvägagångssätt jämförs: ett aggregerat tillvägagångssätt och ett detaljerat tillvägagångssätt nära underhållstidpunkterna. Vi analyserar beräkningstiden och lösningens kvalitet på en verklig tidtabell med olika underhållsscenarier. Resultaten visar att medan det aggregerade tillvägagångssättet är användbart för att hitta rimliga tidsluckor, så är det detaljerade tillvägagångssättet nödvändigt för att hitta lösningar med hög kvalitet och minsta möjliga trafikpåverkan. I det andra steget minskar vi beräkningstiden med hjälp av konstruktionsheuristik. Vi använder en algoritm för att hitta realistiska underhållstidpunkter kombinerat med en fixeringsheuristik för tågen. Våra experiment visar att dessa heuristiker avsevärt minskar beräkningstiden (med mer än 50% för de studerade testfallen) för lösningar av likvärdig kvalitet. Begränsningar av modellen och förbättringar diskuteras.