Transport is one of the most important sectors of the national economy, which completes the manufacturing sector, is essential to the development of trade, and also has an impact on the population social development, i.e. the development of tourism and reduction of unemployment. Additionally, it enhances regional development and provides access to various services. On the other hand, transport creates significant external costs, which are wholly or partly covered by the public. The highest costs are generated by road transport, much lower by inland shipping, railway and sea transport.1 Although there is a common consensus concerning the overall objectives: dealing with “fair and efficient pricing”, a transport system contributing to “a smart, sustainable and inclusive economy”, their practical realization encounters many problems and is far from straightforward. There are some publications relating to the valuation of external costs of inland shipping [4,5] but none of them analyzes specific aspects of inland waterway transport in Poland. This paper deals with the problem of assessing the benefits of the waterway infrastructure development in Poland and the proposed method of assessing the external costs of road and inland waterway transport, as an essential element in the assessment of the social benefits of each infrastructure investment.