Resumen
A transportation network is a layout of connections, in a region, between communities of people developed in the course of interaction of economic and social, as well as natural environment factors. The current form of transportation network is the result of long term development, which started with the first settlements in the region. When in the course of history, a modernization or an expansion was done, it was to fulfil the new transport requirements, and the work was based on the current structure of the transportation network. These temporary requirements mostly arouse due to random factors which as time went by ceased to prevail. As a consequence the structure, as a rule, is not optimal. At the moment, we can observe a steep increase of communication needs associated with the intensification of economic growth, rising affluence of society and urbanization of new areas. The paper deals with the problem of the transportation network development in response to the new demands. The task is to minimize the total network impedance taking into account the constraints of the investment budget. A bi-level model of the transportation network consisting of some classes of road links was developed. At the upper level the objective function is the usage cost expressed by the total travelling time. At the lower level, at each procedure step the optimal distribution of the traffic is searched for. The main aim was to indicate the most advantageous and acceptable directions of development of the transportation network.