2.1. Estimation of empirical trip generations
As an input data for modelling purposes empirical trip generations has to be obtained. In this paper two
sources of data were used: comprehensive travel study in Kraków metropolitan area (KBR Kraków (2007)) and
comprehensive travel study in the city and district of Poznań (KBR Poznań (2000)).
Within the comprehensive travel study in Krakow metropolitan area questionnaires in firms using trucks were
done. In 33 communes located in area of the survey 100 firms were inquired. In fact, the questionnaire was a trip
diary that identifies trips origins, destinations and purposes. Extension of survey results to population gave
confusing results. In some communes no truck trips were indentified. Hence, a different approach was
introduced. Based on results of questionnaires, average number of daily trips made by light and heavy trucks was
calculated. Only trips that have either origin or destination outside particular commune were considered. In
average, light trucks carry out 1.91 trips daily, while heavy trucks – 2.34. In the next step the number of trucks
registered in each commune was obtained. Then, the number of trucks in each commune was multiplied by
average number of daily trips. Those were made for both types of trucks. Described procedure resulted in
empirical trip generations. This method might be called the direct method.
A different approach, called indirect method, was used in district of Poznań. The area of the survey covered 17
communes. Based on large set of roadside interviews initial O-D matrix was developed. In the next step elements of O-D matrix were calibrated to minimize difference between measured and modeled traffic volumes on links.
Last step was summing O-D matrix rows and columns to get productions and attractions for each commune.