In the Oslo area short period traffic counts on trains (NSB) are used to assess annual traffic volumes and changes from year to year. This report is an evaluation of the procedures used in handling and drawing conclusions from the short period counts. It includes a statistical analysis of the uncertainties inherent in the procedures with emphasis on sample size and the importance of correct expansion factors. The traffic count data from NSB contain certain inconsistence between the number of passengers from/to railway stations, and the total number of passengers on certain route sections. Relative changes in traffic on route sections can differ from changes in total number of passengers and passenger transport work within relevant areas. It is recomended to use a larger number of counting days, and to introduce new methodological tools in order to calculate changes in the potential income for the traffic company.