As in most developing countries, the resources available in Mexico for improving the infrastructure of the transportation system and its services are frequently insufficient. This situation has led the Mexican Transport Institute (MTI) to develop strategies for optimizing the allocation of resources among the various necessities of the system. The use of the economic value of the freight flows for identifying and planning improvement projects to be undertaken for a specified time period on basic surface transportation networks (roads and railways) is proposed. This parameter can also be used for assessing the relative importance of the components of such networks. The methodology suggested for assessing the economic value of the freight flows is presented. The basis of the use of the criterion proposed including its greater convenience than other commonly used criteria (of the benefit/cost type) is described. Based on the suggested criterion, several considerations are raised for the Mexican road and railroad networks. The belief of some policy makers that freight is of paramount importance for planning improvements to the transportation systems is applied and facilitated by the applications described.