Grain bypasses Greater Odesa. Which route leaves the smallest carbon footprint?

The shortest route for Ukrainian grain to reach many of its traditional destination markets runs through the ports of Greater Odesa. When Pivdennyi, Chornomorsk and Odesa operate normally, grain travels a relatively short distance overland before being loaded onto bulk carriers bound for North Africa, the Middle East and Asia. Their advantage lies not only in deep-water capacity, but also in a location well suited to the geography of Ukrainian grain trade.

The war has disrupted this logistical simplicity. Repeated attacks can raise risks to crews, vessels and cargoes to the point where shipowners become reluctant to accept new bookings. Grain must then be redirected through Ukraine’s Danube ports, Romania’s Constanța, the northern Adriatic, or ports on the Baltic and North Seas.

A detour means more than higher costs and longer delivery times. A comparatively direct supply chain is replaced by multimodal arrangements involving rail, inland waterways, maritime transport and additional transhipments. The journey becomes longer, and so does its environmental footprint.

The relevant question is therefore not simply how Ukrainian grain can be exported when Greater Odesa becomes constrained. It is also how emergency flows should be routed so that they leave the smallest possible carbon footprint.

Three quantitative studies provide complementary answers. Together, they examine the allocation of different grains, the effects of expanding individual terminals and ports, and the way the European transport network responds as Ukrainian wheat transit grows. Their common message is clear: geography strongly favours the south, but efficiency alone is not enough to guarantee resilience.

The entire journey matters

Comparing only the distance from the Ukrainian border to the nearest seaport can be misleading. The whole transport chain matters: from the point at which grain enters the analysed network, through rail and inland waterways and the necessary transhipments, to the final sea voyage to the recipient.

Entry points included facilities close to the Ukrainian border as well as inland hubs connected to Ukraine by broad-gauge rail, such as Sławków in Poland and Košice in Slovakia. Grain was then transported to ports on the Black Sea, Adriatic, Baltic or North Sea and finally shipped to markets traditionally served by Ukrainian exports.

Each section of the route was assigned greenhouse gas emissions per tonne of cargo. These values depended on transport mode, distance and terminal operations. Adding the emissions generated on successive legs made it possible to compare complete transport chains rather than individual links.

The system boundary was deliberately limited. The models did not include transport across Ukrainian territory before the grain reached the analysed entry points, nor distribution after unloading at the destination port. Within that boundary, however, all relevant legs were assessed together. This matters because a route that looks attractive when only the European inland section is considered may lose that advantage once the sea voyage is added.

Capacity constraints were equally important. Border terminals, river ports and seaports cannot handle unlimited quantities. Once the most favourable connections are fully utilised, additional flows must be redirected along less attractive routes. In the most comprehensive model, Ukrainian transit also shared infrastructure capacity with wheat exports originating in the EU countries.

The three studies asked different but complementary questions. The first compared the optimal allocation of maize, wheat and barley in separate scenarios. The second tested where additional handling capacity would produce the largest reduction in emissions. The third examined how an increase in transit volume changes the structure of export corridor use and whether the least-cost configuration differs substantially from the lowest-emission one.

The models are therefore not timetables for trains, barges or vessels. They reveal the structure of the system: which routes are preferable, when they begin to run out of capacity and which alternatives must then be activated.

Geography favours Constanța

Across the analyses, the southern corridor through Romania’s port of Constanța emerged as the strongest option. The first advantage is the relatively short inland journey. Dornești, for example, lies close to the Ukrainian–Romanian border and is connected to Constanța by a comparatively short rail route. Moving one tonne of grain from Dornești to Constanța is estimated to generate about 8.9 kilograms of carbon dioxide equivalent. Comparable routes from Záhony in Hungary or Sławków in Poland to Trieste generate around 12.2–12.4 kilograms.

The second advantage begins after the grain reaches the coast. Constanța is favourably located in relation to many traditional destination markets for Ukrainian grain. Vessels bound for Turkey, Egypt, Israel, Saudi Arabia or Asian destinations start their voyages in the Black Sea instead of sailing around Western Europe. Transporting one tonne of cargo by sea from Constanța to Alexandria generates just under 11.1 kilograms of CO₂ equivalent. The corresponding figure is about 13.6 kilograms from Trieste and between 36.6 and 40.2 kilograms from Hamburg, Szczecin or Gdynia.

The corridor through Romania also benefits from the Lower Danube. Grain can reach Constanța by barge from the Ukrainian ports of Reni and Izmail, travelling to Cernavodă and then through the Danube–Black Sea Canal. For bulk cargo, inland waterway transport is especially valuable because it can move large volumes with relatively low energy use per tonne.

Taken together, these features make the funnel-shaped southern corridor through Constanța highly efficient in both environmental and economic terms.

Its advantage is not universal. Ports in the Adriatic may be more favourable for some Western Mediterranean destinations, and the final outcome depends on where the grain is sold. Nor is the southern route through Constanța immune to disruption. During periods of low water, reduced permissible draught limits the load carried by each barge, while extremely low levels can require reducing the number of barges in a convoy. The record-low Danube levels observed in the summer of 2026 therefore increased the importance of rail alternatives.

Different grains travel differently

Ukrainian grain is often discussed as though it were a single, homogeneous flow. In reality, maize, wheat and barley are sold in different proportions to different parts of the world. Their trade geography therefore influences the optimal transport pattern.

One of the studies reconstructed the principal pre-war destination markets for each of the three grains and then determined how flows should be allocated between entry terminals and EU ports so as to minimise emissions. In all three cases, the southern corridor through Constanța played the central role, but not to the same extent. Maize and barley were heavily concentrated on the southern route. Wheat was distributed more broadly, with a larger share passing through northern Adriatic ports and entering the EU network through Hungary and Slovakia.

The explanation is not that a tonne of wheat transported along the same route produces different emissions from a tonne of barley. The difference comes from destination markets. A port well placed for one group of buyers may be less suitable for another. Constanța has a strong advantage in serving the Eastern Mediterranean and many Asian markets, while Adriatic ports can be more favourable for destinations farther west.

The scale of demand in individual markets also matters. If a major buyer of a particular grain can be served most efficiently through one port, that market can draw a large share of the modelled flow onto a specific corridor. Once the relevant terminal or port reaches capacity, however, remaining deliveries must be redirected elsewhere. The resulting pattern therefore reflects the interaction of three elements: where the buyers are located, the emissions associated with individual routes and how much traffic the infrastructure can actually handle.

This has practical implications. Two marketing years with similar total export volumes may place very different demands on the transport system if the proportions of maize, wheat and barley change or if the geography of sales shifts. Planning therefore requires more than an estimate of how much grain must leave Ukraine. It also matters which grain is being transported and where it is going.

Which terminal should be expanded first?

A second study asked a different question: if several terminals are already operating at full capacity, which one should be expanded first? Intuition suggests that facilities already operating at their limits are the most urgent candidates. The model showed that this is not necessarily the case. Full utilisation and the environmental value of additional capacity are two different things.

The capacity of each fully utilised terminal or port was increased separately by 250,000 tonnes per year, after which the lowest-emission configuration was recalculated. This revealed where additional capacity could shift grain from higher-emission routes to more favourable ones.

The contrast between Medyka and Dornești was particularly revealing. In the baseline solution, the Polish terminal at Medyka used all the capacity assigned to it. Yet increasing its capacity did not reduce total emissions. Additional capacity there did not unlock a more favourable complete route.

By contrast, expanding the Romanian terminal in Dornești allowed more grain to use the short connection to Constanța and reduced reliance on less efficient alternatives. Under the model’s assumptions, this produced the largest reduction in emissions among the tested expansions: about 39 tonnes of CO₂ equivalent for every additional 1,000 tonnes of annual handling capacity.

The point is not that expanding Medyka would be pointless. Additional capacity could improve reserve capacity, reduce queues or help during disruptions. The narrower conclusion is that a terminal operating at its limit is not necessarily the node whose expansion brings the greatest environmental benefit. The value of additional terminal capacity depends on the existence of a complete corridor.

 

What happens as grain volumes increase?

The third study examined how the shared European network responds as Ukrainian wheat transit gradually increases. This model also included wheat exports originating in the EU countries through which the Solidarity Lanes pass. These EU-origin wheat exports had to be handled in full, while Ukrainian transit could use the remaining capacity of terminals and ports. The model therefore asked how much additional Ukrainian wheat could be introduced into an already functioning network.

At an annual transit volume of 4.2 million tonnes, more than 99 per cent of Ukrainian wheat was routed through the southern corridor via Constanța. Reni, Izmail, Romanian rail entry terminals and Constanța itself played the principal roles.

As transit volumes increased, however, the southern corridor through Constanța approached its limits. The Ukrainian Danube ports were the first transit entry nodes to reach their capacity limits. Additional flows then had to use other entry terminals and seaports. At around 6.7 million tonnes of annual wheat transit, the Adriatic’s share had already become significant. Further growth required increasing use of the Baltic corridor. The network progressively brought less favourable connections into use as the best ones filled up.

Under the model assumptions, the network reached its limit at approximately 8.8 million tonnes of Ukrainian wheat transit per year. This was not an estimate of the EU’s total capacity to handle all Ukrainian grains, but a threshold for wheat within the specific network and capacity assumptions adopted in the model.

The limit did not result from one port becoming completely saturated. Small amounts of spare capacity remained in various locations, but they were geographically dispersed and could not be combined into another complete route from entry point to destination market.

At the maximum feasible level of transit, the southern corridor through Constanța still handled around 66 per cent of the Ukrainian flow. The Adriatic accounted for approximately 21 per cent and the Baltic for 13 per cent.

This leads to an important conclusion: the Adriatic and Baltic routes did not replace the southern corridor via Constanța. Instead, they allowed for additional exports once the most advantageous connections via Romania had reached their capacity limits.

Efficiency and resilience

This is where efficiency begins to come into tension with resilience. At lower volumes, concentrating flows on a small number of southern routes shortens the journey, reduces emissions and makes regular services easier to organise. But it also increases dependence on a limited number of ports, terminals and waterways.

When volumes increase, or when one of the main nodes is disrupted, longer routes through the Adriatic and Baltic become necessary. At high transit volumes, they are no longer merely reserve options. They become essential to the system’s ability to handle the assumed flow.

The same logic applies to disruptions. An attack, technical failure, low water or congestion affecting one critical component can disrupt a substantial share of exports. Alternative corridors therefore have value even if they are less efficient under normal conditions.

Resilience does not mean using every route equally. It means keeping alternative corridors operational and capable of absorbing traffic when the main corridors become congested or unavailable.

Is the cheapest route also the greenest?

One further question is whether the lowest-cost configuration differs greatly from the lowest-emission one. For the scenario with the maximum feasible transit of Ukrainian wheat, the model was solved twice. First, it identified the least-cost configuration. The second run used the same flows and capacity constraints but minimised greenhouse gas emissions.

The difference was surprisingly small. In the least-cost solution, total transport costs amounted to approximately 1.752 billion euros and emissions to about 858,700 tonnes of CO₂ equivalent. When the objective was changed to emissions minimisation, emissions fell to around 857,100 tonnes, a reduction of only 0.2 per cent. Total costs rose to about 1.759 billion euros, an increase of less than 0.4 per cent.

The two allocations were not identical, but their overall geography remained similar. Shorter routes and efficient waterborne transport tended to reduce both costs and emissions.

This does not mean that the cheapest configuration will always be almost as green as the emissions-minimising one. The result applies to a particular network, set of cost assumptions, emissions factors and capacity constraints. It does show, however, that the larger policy tension in this case is not between economic and environmental optimisation.

The composition of the footprint also helps explain why changing ports alone offers only limited scope for further improvement. In the maximum-transit scenario, almost 88 per cent of emissions came from maritime transport. Ships are relatively efficient per tonne-kilometre, but the distances involved in the sea leg are much greater than those travelled by trains and barges within the European network.

If deeper reductions are sought, reallocating cargo among existing corridors will therefore not be enough. More energy-efficient vessels, lower-carbon electricity for railways and terminals, better use of carrying capacity, fewer empty movements and more efficient transhipment operations would also be needed. Network optimisation can exploit the strengths of the existing system, but it cannot substitute for technological decarbonisation.

The larger policy tension lies between concentrating flows on a small number of highly efficient routes and maintaining enough alternatives to preserve resilience.

A terminal cannot be expanded in isolation

All three studies point to the same conclusion: the performance of a corridor is determined not by its largest port or most efficient terminal, but by the availability of a complete route from entry point to destination market.

European infrastructure policy should therefore focus on coordinated investment packages rather than isolated facilities. Strengthening a single terminal will achieve little if the railway, inland waterway, port or onward maritime connection cannot handle the additional cargo.

The findings primarily support strengthening the southern system as a whole. Particularly favourable results could come from increasing the capacity of the Ukrainian river ports of Reni and Izmail and Romanian rail terminals while further integrating the Lower Danube system, rail transport and the port of Constanța.

This does not mean that investments should be made only in Ukrainian Danube ports and in Romania. Concentrating flows on the shortest routes reduces costs and emissions, but it also increases dependence on a limited number of facilities. An attack, technical failure, period of low water or congestion at one key component may then disrupt a large share of exports.

The Adriatic and Baltic corridors therefore serve a different purpose. They need not handle the largest volumes to remain strategically important. At lower transit levels they are less attractive, but as flows rise they become essential. They also provide insurance against disruption in the south.

A rational infrastructure policy should therefore pursue two objectives at once: strengthen the connections with the best environmental and economic performance, and maintain sufficient capacity on alternative routes even if they are longer and used less frequently.

The models do not provide a ready-made investment timetable. They simplify the real transport network and do not reproduce every source of congestion, rolling-stock shortage, weather disruption or seasonal concentration of flows. What they do reveal are relationships that remain invisible when each facility is assessed in isolation: a fully utilised terminal is not always the most important bottleneck, spare capacity does not necessarily form a usable corridor, and the lowest emissions do not always coincide with the greatest resilience.

War has forced Ukrainian grain to take a detour, but there is no single detour suitable for every cargo and every level of exports. The Constanța corridor remains the foundation of the lowest-carbon and lowest-cost system; the Adriatic adds capacity, while the Baltic widens its margin of safety.

The question for Europe should therefore not be limited to which terminal to expand. It should be which complete export corridors it wants to preserve for the next disruption.

The authors declare no conflicts of interest. Neither the preparation of this article nor the three underlying studies received specific external funding or support from any sponsor or commercial partner.

Adrian Sadłowski holds a doctorate in economics and is an assistant professor at the Institute of Economics and Finance at Cardinal Stefan Wyszyński University in Warsaw. His research focuses on agricultural policy, agri-food trade and the logistics of agricultural products.

Vivien Ágnes Nagy is a researcher affiliated with the Hungarian University of Agriculture and Life Sciences. Her research interests include management, logistics and supply-chain operations, as well as the role of the bioeconomy in achieving the Sustainable Development Goals.

Mihaela Popa is a professor of transport engineering at the National University of Science and Technology Politehnica Bucharest and director of its Doctoral School of Transport. She specialises in transport-system planning and modelling, intermodal transport, logistics and the resilience of transport networks.

Zoltán Károly Lakner is an economist and a professor at the Hungarian University of Agriculture and Life Sciences. He is also affiliated with Tashkent State Agrarian University. His research focuses on the food economy and agricultural policy, as well as on the modelling of socio-economic systems and the resilience and management of food supply networks.