Technological innovations in the Dutch railway sector, such as ERTMS and the 3kV power supply system make it possible to increase the efficiency, effectivity and speed of the railway system in the upcoming decades. The implementation of systems such as ERTMS and 3kV is a lengthy process. The new systems will therefore operate alongside the old systems (ATB-EG and 1.5kV) for a long period of time. Between the old and the new system, operational transitions are required. The number of operational will therefore increase in the coming years. Some of these transitions from one system to another system turn out to be prone to failures and disruptions. When an operational transition fails, this can cause considerable delays on the railway network. Especially when multiple operational transitions are close together and occur nearly simultaneously, the risk of failures in one of these transitions is present. When operational transitions are combined, a failure in one transition can have large effects on another operational transition that is about to take place. Operational transitions are defined by two characteristics. Firstly, they are physical locations in the rail infrastructure. Secondly, operational transition require the driver to switch between two systems, or to change his/her behaviour significantly. The aim of this thesis is to investigate the effect of operational transitions on the reliability of train operations. The magnitude of the impact of operational transitions on the reliability of train operations is often unclear. This thesis contributes to scientific literature by examining a sizable number of operational transition types and providing an initial insight into the effect of these transitions on railway operations. For society in general and for ProRail in particular, the findings of this research can contribute to a better understanding of operational transitions. Using the acquired knowledge, ProRail can take measures that increase the reliability of operational transition passages, thereby increasing the punctuality of train services.