The paper presents a technical station model using the graphical evaluation and review technique – GERT. The network model reflects the operation of trainset service in compliance with the technology and technical equipment as well as interaction between technological systems at the service stations that are different by track development but connected to big passenger stations, which gives a possibility of determining the service time of trainsets depending on the number of carriages and the specificity of operation conditions. This GERT model is applied to the case study of an individual service station within the railway network in Bulgaria. The regression functions of service time are worked out according to the type and the number of carriages taking into account the limitation parameters. The functions obtained could be used for trainset scheduling to optimize the operation of passenger carriage fleet.