Developing accurate and reliable transportation models capable of simulating real traffic behaviour is essential to making sound engineering and investment decisions. However, the construction of transport models is typically data- and time-intensive, opaque, and the results are not reproducible. This paper describes the development of the passenger component of the new macroscopic four-step National Transport Model (NTM) for Slovakia. Efforts were made to limit the number of dimensions of the model as far as possible, beginning with one demand stratum and increasing complexity only with improved model fit. Traditional data sets, such as national registries, censuses, and travel use surveys, were compared to novel data, such as public transport ticket sales, mobile phone GPS signals (call detail records), and open-access data sets for cross-border travel. Finally, validation against several existing models was conducted. The result is a passenger traffic model with 25 demand strata, 109 domestic zones, and 68 international zones. This is a significant simplification relative to the previous National Model. The aim of the new NTM and this paper is to increase transparency and reproducibility of transport models.