Trams are regarded as one of the most robust forms of urban transport. However, the extreme heatwave in June 2026 demonstrated that even modern tram systems can be vulnerable to climatic extremes. In Leipzig, an unusual failure pattern affecting trackwork and points led to an almost complete suspension of tram services across the network. Particularly noteworthy was the fact that the recovery of operations relied not only on specialist technical equipment, but also on the support of numerous local residents who assisted in restoring the infrastructure.

The incident raises fundamental questions: How heat-resistant are tram networks in Germany? What structural solutions are required? And do cities need to reassess their infrastructure in the face of increasing extreme temperatures?

The cause of the disruptions in Leipzig was not down to the vehicles themselves, but to the track infrastructure. Temperatures of around 40 degrees Celsius caused the joint sealants and grouting materials between the rails and the road surface to soften. The liquefied material seeped out in areas around the rails and points, was spread by the trams and formed sticky layers on the track surface. As a result, the trams were no longer able to operate safely.

It should also be noted that rail temperatures were significantly higher than the ambient air temperature. While air temperatures in Leipzig reached around 40°C during the heatwave, rail temperatures of up to 70°C were recorded in some parts of the network. Such extreme thermal loading significantly accelerates the softening of bitumen-based rail sealing compounds. Traditionally, many German tram systems have used bitumen as the sealing material between the rail and the surrounding road surface. However, with increasingly frequent periods of extreme heat, a growing number of operators are evaluating polymer-based sealing compounds, which offer improved resistance to high temperatures and weathering, thereby enhancing the long-term resilience of embedded tram track infrastructure.

Leipzig Transport Authority (LVB) was therefore forced to suspend tram services completely for a time. Passenger safety was the top priority whilst the affected sections of track were inspected and cleaned. An expert then began carrying out material analyses, the results of which are also to be taken into account in future construction projects.

The damage highlights a fundamental problem affecting many inner-city tram routes: the tracks are often laid within traffic areas made of asphalt or concrete, materials which are subject to high thermal stresses. Areas with heavy traffic, tight track curves, points and poorly ventilated street spaces are particularly critical.

The incident in Leipzig took on an unusual dimension due to the involvement of the local community. LVB called on members of the public to help remove the softened joint sealant using scrapers and other tools. Numerous volunteers assisted the transport company’s staff in cleaning key sections of the route.

The operation demonstrated a special form of collaboration between the transport authority and the wider community. At the same time, however, it also highlighted the extraordinary nature of the situation: a highly complex transport system had to be restored to working order, in some cases with manual assistance.

For local public transport, this is an important aspect of climate adaptation. In addition to technical solutions, new organisational approaches may also be required in future – such as additional on-call services, rapidly deployable repair teams or closer involvement of local stakeholders.

The tram service disruption had a significant impact on Leipzig. The tram is the backbone of the city’s public transport system and connects numerous residential areas with the city centre, workplaces and key facilities.

During the disruption, buses had to provide a replacement service. However, this was only possible to a limited extent, as the bus fleet does not have sufficient capacity to replace the entire tram network at short notice. Furthermore, the extreme heat also took its toll on the roads and vehicles.

The incident made it clear that the resilience of public transport does not depend solely on vehicles and operational technology. The entire infrastructure chain is crucial – from track construction and energy supply to workshops and staff planning.

The damage in Leipzig was not an isolated incident. Other German tram operators also reported heat-related problems. Nuremberg was particularly affected, where softened bitumen and jointing material also led to significant disruption. Cleaning the trams and tracks was a labour-intensive process; in some cases, specialised equipment such as dry ice had to be used.

Heat-related disruptions were also reported from Würzburg and Bremen. The nature of the damage was similar: extreme temperatures caused materials in the track area to lose their intended properties.

This reflects a nationwide trend: tram networks, which were planned decades ago based on historical climate conditions, will have to cope with significantly higher temperature peaks in future.

However, the effects vary depending on the grid structure and construction method:

The extensive network, which includes numerous sections at street level, is heavily dependent on the quality of the track bedding. Downtown areas with heavy traffic and many switches are particularly critical.

Here, too, softened material led to operational problems. The situation demonstrated that similar construction methods can be vulnerable regardless of a city’s size.

Some of these cities have extensive rail networks with different types of track structures. The key factor is the proportion of modern, dedicated tracks compared to tracks integrated into the road network.

The capital city’s extensive tram network has numerous dedicated tracks, which partially reduces the direct impact of heated road surfaces. Nevertheless, switches, stop areas, and embedded tracks remain critical points.

Rising temperature peaks are presenting transport operators with new challenges in the planning, construction and maintenance of tram infrastructure. In future, track designs and the materials used will need to be better adapted to the expected climatic stresses. This will include, in particular, reviewing existing sealing and infill materials for their temperature resistance, as well as developing and testing alternative materials that retain their mechanical properties even during periods of extreme heat.

Furthermore, climate change is likely to influence future procurement and design standards. New-build and renewal projects will have to consider not only conventional requirements such as load-bearing capacity, vibration reduction and durability, but also resilience against increasingly frequent temperature extremes. At the same time, adapted maintenance and monitoring strategies will become more important in order to identify critical areas, such as points or heavily used sections of embedded track, at an early stage and enable targeted responses when required.

The incident in Leipzig thus demonstrates that the availability of a tram network does not depend solely on vehicle technology and operational organization. Even seemingly insignificant components of the track structure can become critical factors for operational safety under extreme weather conditions. Climate adaptation is therefore becoming an ongoing challenge in tram construction and infrastructure planning.

The disruption to Leipzig’s tram network is more than a local infrastructure issue. It demonstrates that adapting to climate change is increasingly becoming a core responsibility for transport operators. Trams will remain a key component of sustainable urban mobility, but to continue fulfilling this role in the future, their infrastructure and operating concepts must be adapted to a new reality: extreme temperatures that were once rare exceptions are becoming foreseeable operational challenges.

The key lesson from Leipzig is therefore clear: the tram itself is not the problem – it is the ability of its infrastructure to adapt to a changing climate that will determine future resilience.

Tram tracks in urban streets are often constructed using embedded track systems, in which the rails are integrated into the road surface with elastic materials and the gaps alongside the rails are filled with sealing and infill compounds. This construction method reduces structure-borne noise, protects the track system and allows trams to be integrated into urban streetscapes. However, these materials are exposed to significant mechanical and thermal stresses.

During periods of extreme heat, certain sealing and infill materials can change their physical properties. If temperatures exceed the material’s design limits, the compound may soften or become partially plastic, allowing it to deform or be displaced under the repeated loading from passing trams. If softened material reaches the rail head, points areas or vehicle components, it can affect operational safety and disrupt services.

During the exceptional heatwave in Leipzig, the high temperatures caused sealing material in sections of the track structure to soften and spread under the loads generated by tram operations. Particularly critical were points areas, where even small deposits or contamination can affect the precise movement of the switch blades and therefore compromise safe vehicle passage. As a precautionary measure, tram operations were temporarily suspended until the affected areas had been inspected and cleaned.

The incident highlights that climate adaptation of tram infrastructure must consider more than just the rails and the primary track structure. Seemingly minor components, such as sealing compounds and track infill materials, can become critical weak points under extreme weather conditions. Future renewal and construction projects will therefore need to place greater emphasis on temperature-resistant materials, adapted construction methods and the consideration of future climate scenarios during design and procurement.

The increasing frequency of extreme heat events represents a new challenge for conventional embedded tram track construction. Systems that have operated reliably for decades must now be designed to withstand higher peak temperatures and more frequent periods of extreme thermal stress.