Fare system modeling in public passenger transport is a complex issue of harmonizing the demands and needs of system users with system capabilities, particularly in integrated transport. The analysis of previous fare systems in integrated transport reveals a lack of research on fare systems from the point of view of transport disadvantage and fare model equity. Transport disadvantage, which refers to both space and society, presents restricted mobility or lack thereof. Public passenger transport presupposes equal accessibility to all its users, as well as the possibility of using it under equal conditions. In previous fare systems, equal accessibility meant equal price per kilometer for each user of the transport service. However, the accessibility did not take into account equal transport, economic, and demographic development of an area in which the service is provided. Having that in mind, fare system models require changes so that transport disadvantage can be prevented in the given arm. The adoption of equity fare models aims to reduce transport disadvantage by favoring the users of the system who are already at a very unfavorable position, intending to ensure equity. Therefore, the following hypotheses are put forward in this dissertation: 1. It is possible to define and evaluate new equity criteria for determining fare zones in integrated passenger transport, 2. It is possible to devise an equity fare system model in integrated passenger transport using the said criteria. Scientific research has identified the equity criteria for determining fire zones in integrated passenger transport. These provide an insight into the development of fare zones from the transport, economic, and demographic aspects. The identification is a prerequisite for determining all equity criteria relevant for establishing fare zones in integrated passenger transport. System dynamics modeling has helped to establish the criteria relevant to an equity fare model which aims to prevent some of the criteria being repeated. The selection of representative indicators (equity criteria) for determining fare zones was made by system dynamics modeling using a causal loop diagram. The definition of equity criteria meets the initial requirement for establishing the impact the criteria have on the cost of fare zones. For the defined equity criteria to be used to devise an equity fare model, the impact of each given criterion must be determined. This was done by assessing the defined equity criteria using the analytic hierarchy process (AHP) methodology as one of the most recognized methods for multi — criteria decision — making. It was based on the rankings of 117 European experts for transport, economy, and demography. The obtained weight coefficients of the defined equity criteria and sub — criteria are the prerequisite for devising an equity fare system model in integrated transport. The model was developed by upgrading the basic mathematical model for calculating the cost of a single journey within a zone by implementing the equity coefficient. The new model introduces the equity coefficient, which comprises the equity criteria and regulates the cost of a fare zone to ensure equality and prevent transport disadvantage. The obtained model has ensured a transition from equality to equity and cost regulation from the aspects of equal transport, economic, and demographic development of each of the zones in the integrated transport. The equity fare model was tested in the Sisals — Moslavina county which represented the most underdeveloped counties in the Republic of Croatia. The region is also characterized by a great number of rural areas and unequal transport, economic, and demographic development. Based on the case study, the model provides an overview of changes compared to the basic fare system. In other words, it outlines the changes based on which public transport service is charged equitably. Apart from the comparative analysis of the basic and equity fare system on the case study, a discussion of the obtained results is also provided. The research has also put forward and confirmed two new scientific hypotheses. Hypothesis one confirms the possibility of defining and evaluating new equity criteria in three stages when determining fare zones in integrated passenger transport. The first stage saw a successful identification of potential equity criteria that affect the fare system: transport, economic, and demographic development of an area. In the second stage, system dynamics modeling and causal loop diagrams were used to define equity criteria for determining fare zones. Finally, in the third stage, the first hypothesis was confirmed in its entirety by assessing the defined criteria using the analytic hierarchy process methodology. The second hypothesis that had been put forward was confirmed after a model of the equity fare system in integrated passenger transport was devised using the new equity criteria. Based on what has been stated above, the scientific contributions of the doctoral research are as follows: • The establishment and evaluation of new equity criteria or determining fare zones in integrated passenger transport, • The development of an equity fare system model based on the newly defined criteria for determining fare zones in integrated passenger transport. The developed model and its adoption ensure service equity by engaging users who are in a more unfavorable position. The disadvantage of transport, social groups, and individuals is reduced from the transport service aspect. Transport demand increases in rural and underdeveloped areas because the transport service cost is adjusted to the area. The mission and vision of public transport are achieved in their entirety as public transport becomes available to all, under equitable, not equal, conditions. Equal conditions refer to the equal price per kilometer of a journey and not the equal quality of the transport service of equal economic and demographic development. This scientific research has created a foundation in the form of the first equity fare system in integrated passenger transport.