The subject matter and research problem of this paper is the study of the development dynamics and trend of the passenger transportation demand in the City of Zagreb public bus transport system. The purpose of the study is to scientifically establish the possibility for applying mathematical forecasting models in management and optimization of the transport process. The aim of the study is forecasting of passenger demand in the public passenger transport system for purposes of the transport operator management. The transport parameter studied here is expressed by the number of passengers carried in the City of Zagreb public bus passenger transport system that is operated by the public transport operator Zagrebački Holding d.o.o. Division Zagreb Electrical Tram. In accordance with the aim of the research, the following hypothesis has been put forward: in forecasting the passenger transportation demand it is possible to apply scientifically proven single-variable mathematical forecasting trend models. The hypothesis has been confirmed. A mathematical forecasting model has been designed that allows us to quantify, i.e. forecast the future passenger demand for transport services. Such transport demand trend model is exceptionally useful to the management of the public passenger transport operator as is allows it to plan, organize and manage its operations. The transport parameter model is represented by a corresponding equation with the respective coefficient of determination. The coefficient of determination is a measure of quality that denotes the level of statistical significance of the description of set data by means of a model equation. The model equation describes the development regularity of the studied transport parameter during the observed period 2004-2008. In creating the model variants, the following scientific methods were used: mathematical statistics, modelling, and the Microsoft Excel computer software.  Index Terms-Trend forecasting model, passenger transportation demand, public bus passenger transport I. INTRODUCTION Public passenger transport is a fundamental prerequisite for the functioning of urban agglomerations Manuscript