Subject and purpose of work: The S16 road corridor is of particular importance for the socio-economic development of the Warmia and Mazury regions. The aim of this article is to assess the economic effects of the modernization of the S16 national road. Materials and methods:: The basic research method used in the study is the cost-benefit analysis method developed by the Road and Bridge Research Institute. Results:: The results of the study indicate economic benefits such as reduction of business costs and improvement of the quality of life of residents, reduction of travel time and vehicle operating costs, improvement of safety, and, on a macro scale, economic development of the region. Conclusions:: The modernization of the S16 national road will contribute to a faster equalization of differences between our region and other well-developed regions of the country, as well as improve the sense of security of the residents of Warmia and Mazury.