This dissertation presents a study about all the costs that fall upon the freight transportation in order to determine the best economic moment to replace transportation equipments. The problem is relevant to the military organization, whose main objective is the execution of logistics for the Army. The mathematical modeling was based on data collect in the military organization and in the Federal System Financial Administration (SIAFI). The development of the model wich includes mathematical equations was supported by bibliography research and data collected in the SIAFI federal system. For the evaluation of the data has used electronic spread sheets of Microsoft Excel was used for the calculation and the fitting of the results. The vehicles considered are used in five large axels of displacements along the national territory. These vehicles have been divided in four categories according to its total gross weight. When the model presented a medium or weak degree of multiple correlation (R2), others mathematical functions have been searched in order to improve the correlation degree. Results are shown in an analytical way and through tables and graphs wich express values in monetary terms as a time function of use of the vehicles.