Nordic rail bottlenecks test Nato’s northern mobility

The extension of Kastrup Airport station, inaugurated this week, is a modest infrastructure upgrade. 

Yet in a Nordic and defence context, it points to a more consequential issue: whether regional rail networks can support the demands now placed on them.

With Sweden and Finland now members of Nato, military mobility across the Scandinavian peninsula has shifted from contingency planning to operational requirement. The ability to move heavy equipment, including armoured vehicles and bulk supplies, into Sweden and onwards to Norway is increasingly central to alliance planning in northern Europe.

Denmark plays a key role as a gateway. 

Rail traffic can move via the Øresund link into southern Sweden and, from the early 2030s, via the Fehmarn Belt fixed link connecting Scandinavia with continental Europe. 

These crossings are often seen as critical enablers. In practice, however, they are not the primary constraint. The limiting factor lies further inland. 

Rail corridors in southern Sweden are already heavily utilised, with limited spare capacity to accommodate additional freight, particularly under surge conditions. In a crisis scenario, this raises practical challenges: competition between civilian and military traffic, delays in deployment timelines, and reduced ability to scale transport volumes when needed.

This imbalance reflects long-standing gaps between cross-border infrastructure ambition and domestic network investment. 

The Fehmarn Belt project, for example, was strongly supported by Sweden, yet corresponding upgrades within Sweden have progressed slowly, if at all. Denmark, by contrast, has invested heavily in rail links to continental Europe, including upgrades to stations and corridors such as Kastrup.

That said, the picture is shifting. 

Swedish authorities, including Trafikverket, assess that current capacity on the Øresund link remains sufficient for expected demand over the coming decades. At the same time, Stockholm has begun allocating substantial funding to strengthen rail infrastructure, particularly in the south, with a growing emphasis on redundancy and resilience.

Industry has also signalled concern. Jacob Wallenberg, a leading figure in Saab’s ownership, has highlighted the risks that infrastructure constraints pose to Swedish industrial competitiveness.

Analysis by the String Megaregion, drawing on work by Sweco, identifies 15 critical bottlenecks across Germany, Denmark, Sweden and Norway. 

Many are expected to persist well beyond the opening of the Fehmarn Belt link. Particular attention is given to corridors such as Oslo-Gothenburg, where limited capacity affects both routine freight flows and the ability to absorb disruption or surge demand.

The implications extend beyond transport efficiency. Persistent bottlenecks risk not only undermining climate targets and constraining trade, but also weakening the resilience of European supply chains.

In the current security environment, they also affect Nato’s ability to move forces and materiel across its northern flank in a timely and scalable manner.

Before Sweden and Finland joined Nato, these infrastructure gaps were largely a national concern with regional economic consequences. They now sit closer to the centre of European security planning.

Seen in this light, the Kastrup upgrade is less an endpoint than a signal: while cross-border links are advancing, the coherence of the wider network remains uneven — and increasingly exposed.