On Monday, the concession companies for the Mont Blanc Tunnel –ATMB on the French side and SITMB on the Italian side – confirmed that the tunnel would be completely closed from September 1 to December 12, 2025. The 15-week interruption to traffic is part of the second test project to renovate the vault, a preliminary stage in a vast modernization program that will extend over several years and is designed to enhance the safety, durability and operational efficiency of this strategic tunnel.

During this phase, some 254 meters of vault, located 8 km from the French entrance, will be completely dismantled and rebuilt. This work will require the complete removal of the tunnel’s safety equipment – surveillance cameras, thermal sensors, incident detectors and ventilation systems – making it impossible to reopen the tunnel partially or alternately during the Mont Blanc tunnel closure period. Specialized teams will be mobilized 24 hours a day to ensure the safety of operations and meet deadlines.

This project follows an initial test carried out in autumn 2024, whichassessed the technical feasibility of the operation andanalyzed its impact on transalpine traffic. The results confirmed the need for further experimental phases before embarking on the complete renovation of the vault, a project estimated to cost several hundred million euros and essential to the longevity of this emblematic infrastructure, which entered service in 1965.

The closure of the Mont Blanc tunnel is part of a global approach aimed at :

• Guarantee user safety with modernized infrastructures and advanced detection systems.
• Modernize facilities and integrate the latest technologies in ventilation, lighting and surveillance.
• Ensure the durability of the structure for decades to come, reducing the need for heavy maintenance in the medium term.

User information and support measures will be put in place, including clearly signposted detour routes, regular notifications to subscribers and real-time communication on traffic conditions. The aim of this planning is to minimize the impact of the Mont Blanc tunnel closure on transalpine traffic, and to guarantee optimum continuity for regular users and carriers.

A strategic France-Italy route at a standstill for 15 weeks

From 5pm on Monday, September 1, 2025 until 5pm on December 12, 2025, the Mont Blanc Tunnel will be completely closed in both directions. The work will involve two sections of vault, located around 8 km from the French entrance, representing a total length of 254 meters to be renovated. This operation is the second test project, following an initial trial carried out in autumn 2024, aimed at determining the optimum operating mode for the complete renovation of the structure.

Inaugurated in 1965, the Mont Blanc Tunnel is one of Europe’s oldest major road tunnels, and a strategic link connecting France and Italy directly across the Alps. Every year, it handles an average of 1,700 heavy goods vehicles per day, essential for trade between Northern Europe and Italy, as well as almost 3,600 light vehicles per day, with summer peaks exceeding 6,000.

The closure takes place in autumn, a period deliberately chosen because of lower traffic levels for light vehicles, which account for almost 75% of total traffic. However, the impact will be significant: according to estimates by the Mont Blanc Tunnel EEIG, almost 90% of heavy goods vehicles will be redirected to the Fréjus tunnel in Savoie, while light vehicles will be split between the Great St Bernard, Fréjus and certain Alpine passes.

The work is part of an unprecedented modernization program: dismantling the vault means removing all the safety systems (ventilation, cameras, incident detectors, thermometer cables). As these cannot be reinstalled on a daily basis, total and continuous closure of the tunnel is the only feasible solution. This experimental project, which alone represents an investment of 50 million euros, is a key step towards the complete renovation of the vault over the next few years.

Why is this work essential?

According to GEIE du tunnel du Mont-Blanc, this is the first major European tunnel to undergo such extensive structural renovation. After 60 years of continuous service, the infrastructure is now in need of major and complex work, both on the slab supporting the roadway and on the vault.

The vault, made of reinforced concrete elements designed in the 1960s, is now showing signs of natural wear, accentuated by :

• theintensity of transalpine traffic (nearly 6,000 vehicles/day during summer peaks),
• extreme temperature variations between winter and summer,
• permanent humidity due to underground conditions.

The work will involve structural reinforcement, upgrading of materials to modern standards, and partial replacement of deteriorated concrete, to ensure the structure’s longevity for decades to come.

To make this operation possible, all overhead safety equipment – ventilation, surveillance cameras, automatic incident detection systems, thermometric cables for fire prevention – must be completely removed. This technical constraint means that even occasional traffic will be impossible during the 15-week construction period. Unlike the regular night-time closures already familiar to users, this time there will be a total, uninterrupted closure.

These experimental projects have a dual purpose:

1. Test different techniques for dismantling and rebuilding the vault, to identify the most efficient and least intrusive method for the existing structure.
2. Evaluate the logistics and safety of an unprecedented large-scale project in an active 11.6 km road tunnel, with all the constraints associated with ventilation, dust evacuation, fire safety and team management in a confined environment.

Ultimately, the experience gained will be used to define the final methodology of the vast modernization program. Valued at several hundred million euros, the program is likely to be spread over several years, and will require repeated closures, probably planned in tranches to limit the impact on cross-border traffic.

The EEIG also stresses themajor safety implications of this project. In addition to improving structural strength, the work will enhance the tunnel’s resilience to fire hazards, an imperative since the tragic accident of March 24, 1999, which claimed the lives of 39 people. The new techniques implemented are designed to raise the tunnel’s safety standards to the most stringent European requirements for underground road infrastructures.

Why a fall closure?

Autumn was chosen for the Mont Blanc tunnel closure because it corresponds to the period of lowest traffic volumes for light vehicles, which account for around 75% of total traffic. This means that disruption to users is limited, and the work carried out by technical teams is safer.

What’s more, autumn weather offers relatively stable conditions for maintenance and renovation work, unlike winter, when frost and bad weather can slow down progress. Concessionaires are mobilizing substantial human and material resources to optimize work progress, with the aim of guaranteeing that the tunnel will reopen on schedule, or even earlier if possible.

Increased safety measures and signposting will be in place throughout the period of closure of the Mont-Blanc tunnel, to inform users and facilitate traffic on the detour routes. Technical teams will also be on hand to adapt the schedule according to weather conditions and the progress of the work.

What are the alternatives for car and truck drivers?

When the Mont-Blanc tunnel closes, traffic will inevitably shift. It is estimated that 90% of heavy goods vehicles will shift to the Fréjus tunnel (Savoie). For motorists, there are several possible alternatives: the Fréjus, Grand-Saint-Bernard or certain Alpine passes, subject to their opening times and weather conditions.

👉 Attention:

• The Col du Petit-Saint-Bernard will be closed from September 22, 2025 for roadworks.
• The Great St Bernard Tunnel will be closed several times at night between August and October, due to work on the Swiss Toules Tunnel.
• Some Alpine passes may be temporarily closed or not recommended for light or heavy vehicles, depending on the weather.

To minimize delays and disruptions, we strongly recommend :

• Plan your journeys in advance and regularly check traffic conditions via applications such as Bison Futé, ViaMichelin or Google Maps.
• which provide up-to-date information on traffic and detour.
• Choose alternative routes adapted to your type of vehicle.
• Take account of closing times and periods at night to avoid any unexpected delays or detours.
• For carriers and regular subscribers, consult customer services or specific subscription notifications for up-to-date information.

These measures are designed to keep traffic flowing despite the Mont-Blanc tunnel closure, and to guarantee user safety during the construction period.

Impact on subscribers

All 10- and 20-pass subscriptions valid on September 1, 2025 will have their validity automatically extended by four months, with no further action required. This measure applies to all season ticket holders, whether they purchased their season ticket recently or several months ago, and is designed to compensate for the period of closure of the Mont Blanc tunnel.

The extension will be applied directly to each subscriber’s account, and no action on the part of users is required. Subscribers will therefore be able to continue to enjoy their usual package once the tunnel has reopened, without losing any passages or rights linked to their subscription.

Customer services remain available to answer any questions about subscriptions or to clarify the details of this extension. This initiative is part of an effort to minimize the impact of the Mont Blanc tunnel closure on regular users, and to guarantee optimum continuity of service for all subscribers.

An investment in the future

These two test construction phases (2024 and 2025) already represent an investment of 50 million euros. Their aim is totest the most efficient renovation methods to guarantee the safety, durability and modernization of the Mont Blanc Tunnel for decades to come, in preparation for the next Mont Blanc Tunnel closure.

The work also provides an opportunity to test new technologies, particularly for ventilation, incident detection, lighting and safety systems. Each phase of the work is carefully planned to minimize the impact on traffic and to validate the techniques before their large-scale deployment, in order to reduce disruption during the Mont Blanc tunnel closure.

In addition, these experiments will help to reduce future maintenance costs and improve the user experience, by guaranteeing safer, smoother traffic conditions as soon as the tunnel reopens. This investment underlinesthe concessionaires’ commitment to maintaining the Mont Blanc Tunnel as a strategic and safe transport route for future generations, even in the event of temporary closure for works.

Closing the Mont Blanc tunnel: a strategic project for safety and modernization

👉 In summary, the closure of the Mont Blanc Tunnel from September 1 to December 12, 2025 will mark a decisive stage in the renovation of this strategic Alpine route. This period of work will make it possible to implement and test new technologies,optimize safety, ventilation and lighting systems, and ensure the overall modernization of the tunnel for decades to come.

While disruption to users will be unavoidable, it is essential to guarantee safety for all, limit the risk of incidents and extend the life of this engineering monument. Specific measures, such as clearly signposted detour routes, continuous information for drivers and support for subscribers, will be put in place to minimize the impact on traffic.

This Mont Blanc tunnel closure is part of an ambitious modernization and preventive maintenance plan, reflectingthe concessionaires’ commitment to ensuring a safe and efficient passage for all users, today and for future generations.

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