Recent disruptions on Berlin’s U1 underground line have once again drawn attention to the condition of the German capital’s transport infrastructure. Speed restrictions, bridge renewal projects and recurring operational disruptions on the historic elevated railway through Kreuzberg highlight the fact that key sections of the Berlin U-Bahn network are increasingly reaching the limits of their technical lifespan. At the same time, Berlin politicians continue to discuss multi-billion-euro underground extensions and even magnetic levitation systems. Developments along the U1 therefore raise a fundamental question: can Berlin realistically pursue new prestige projects while its existing infrastructure faces a substantial maintenance backlog?
More than 120 Years of Infrastructure
The U1 is Berlin’s oldest underground railway line. Large sections of the elevated railway between Warschauer Straße, Schlesisches Tor, Görlitzer Bahnhof, Hallesches Tor and Gleisdreieck were constructed between 1901 and 1902. Numerous viaducts, steel bridges and supporting structures are therefore now more than 120 years old.
Particularly critical is the section between Gleisdreieck and Nollendorfplatz, where several elevated viaducts require comprehensive renewal. At the same time, planning approval procedures are underway for the replacement of several bridge structures, including the Dennewitz Bridge. According to BVG, extensive works are required to ensure the long-term structural integrity of these historic structures.
In addition to the engineering structures, track, power supply systems and station facilities are also approaching the end of their technical service life. The U1 therefore serves as a representative example of many parts of Berlin’s small-profile underground network.
New Speed Restriction as a Symptom of the Maintenance Backlog
The extent of the problem became apparent again in early June 2026. A speed restriction was introduced between Kottbusser Tor and Hallesches Tor, limiting trains to just 25 km/h. In order to stabilise operations, BVG shortened U1 services to Nollendorfplatz on weekdays, requiring passengers travelling towards Warschauer Straße to change to the U3.
BVG cited necessary infrastructure maintenance works as the reason for the restriction. While the measure may appear relatively minor at first glance, it is yet another example of how ageing infrastructure is increasingly affecting day-to-day operations. For passengers, such measures mean longer journey times, additional interchanges and reduced reliability.
Significant Renewal Requirements for Track and Infrastructure
According to BVG, between six and ten kilometres of track need to be renewed annually in order to maintain the network in a stable condition. In practice, the following amounts were renewed:
- 2023: ca 8.5 km of track work
- 2024: ca 6.7 km,
- 2025: ca 8.0 km.
For 2026, only six kilometres are planned, with investments of around €25.6 million allocated to the programme.
These figures demonstrate that BVG has only recently returned to the level of renewal required to maintain the network sustainably. Many of today’s major infrastructure projects are the result of maintenance requirements that have accumulated over several decades.
Nollendorfplatz as a Warning Sign
The fragility of the infrastructure became particularly evident during the four-month closure of Nollendorfplatz station in early 2026. Severe damage to an intermediate structural slab required services on the U1 and U3 to be suspended, while the U4 was completely withdrawn from service.
Approximately €4.3 million was invested in the repairs. Around 560,000 daily passengers using the U1, U3 and U4 were affected by the disruption. The incident highlighted the extent to which individual infrastructure deficiencies can impact the wider network. The fact that one of the most important junctions on the small-profile network had to operate under severe restrictions for several months has been widely viewed as a warning sign regarding the condition of other ageing assets across the Berlin U-Bahn system.
“Stability Before Growth”
Notably, BVG itself has now undertaken a strategic shift in priorities. Under the slogan “Stability Before Growth”, the company announced in 2025 that it would focus first on addressing the infrastructure shortcomings that have accumulated over recent years. New depots, workshops, stabling facilities, signalling systems and, above all, the renewal of ageing infrastructure are to take priority.
Investment rose to more than €530 million in 2025 and is expected to exceed €1 billion in 2026. However, a substantial proportion of these funds is being directed towards the renewal and safeguarding of existing infrastructure rather than network expansion.
This change in priorities demonstrates that the scale of the challenge has now been fully recognised within BVG. Maintaining reliable operations on a network that is, in places, more than a century old requires enormous financial and human resources.
The Wider Context
The investment challenge extends well beyond BVG itself. A study by Investitionsbank Berlin estimates that Berlin’s infrastructure will require approximately €108 billion in modernisation investment over the next ten years. Of this total, around €17 billion relates to public transport.
The challenges range from bridges and tunnels to stations, track infrastructure, depots, workshops and signalling systems. The U1 is merely the most visible example of a much broader investment requirement across Berlin’s transport network.
Commentary: Between Reality and Future Visions
This is where a contradiction in Berlin’s current transport policy becomes apparent. While BVG must invest billions of euros in the renewal of viaducts, tunnels, stations and track infrastructure—and while Germany’s oldest underground railway line can only remain operational through costly replacement projects—the Senate continues to discuss:
- extensions of the U7 and U8 lines;
- long-term visions for a substantial expansion of the underground network;
- magnetic levitation systems as a new transport mode;
- additional multi-billion-euro railway construction projects.
There is no doubt that Berlin will require additional public transport capacity in the long term. However, the U1 illustrates that the city’s most pressing challenge is currently not expansion, but asset preservation.
An elevated railway more than 120 years old, whose bridges require replacement, whose passengers are regularly affected by speed restrictions and whose key junctions have been closed for months at a time demonstrates a simple reality: before new tunnels are bored or magnetic levitation systems are planned, the foundations of the existing network must first be secured.
The most important infrastructure project is often not the construction of a new line, but the timely renewal of the old one. The U1 in Kreuzberg serves as a daily reminder of that fact.
09.06.2026
