International transport corridors (ITC), as the main element of the formation of a new geo-economics, are becoming the most important object of research and development. Their impact on the economic growth of the countries adjacent to the routes, on the efficiency of cargo owners, transport operators, carriers, and infrastructure owners has no clear theoretical or empirical estimates. The purpose of this study is to substantiate and calculate the synergy effect indicator of transport connectivity of the North – South ITC, namely, to assess the maximum volumes of cargo transported along all ITC routes, taking into account the factors limiting its throughput and carrying capacity. Research methods: the scenario forecast for the development of the ITC was obtained by sampling — scenario distribution. In calculating the indicators for assessing the economic effects of the ITC routes, the method of comparing digital data with risk factors limiting rail freight flows was used. The analysis of the distance matrix for three ITC routes was used. The forecast of the estimated indicators is made by the method of dynamic analysis of successive series of indicators of rail freight transportation, characterizing each route, their changes over time. Results: based on the following indicators: throughput and carrying capacity of the ITC railway infrastructure; sustainable development index of the countries of the region; logistics index (customs and border clearance; quality of trade and transport infrastructure); “transportation costs” — the contingency effects were calculated, reflecting the maximum volumes of transported goods, taking into account the connectivity of infrastructure and modes of transport along all routes of the North – South ITC. Practical significance: scenario calculation of contingency effects along the ITC routes can be used in projects for he development of the transport and logistics infrastructure of the ITC, since it allows assessing the effects of growth in freight throughput.