The Mont Blanc Tunnel is preparing for a lengthy shutdown that will have unavoidable repercussions on transalpine traffic. From Monday 1 September 2025 at 5 pm until Friday 12 December 2025 at 5 pm, the road tunnel will be entirely closed to vehicles to allow for the restoration of the vault. This suspension, lasting around fifteen weeks, has been announced by the Geie of the Mont Blanc Tunnel and is part of a programme of trial worksites launched last year, intended to become an operational model for the future maintenance of the infrastructure. The need to ensure the safety and long-term durability of the structure has led to the scheduling of this second experimental project, following the one carried out in autumn 2024.
The intervention will focus on two sections of the vault, totalling 254 metres, located about eight kilometres from the French entrance. The complexity of the work, which involves dismantling the technological and safety equipment installed on the vault, makes it impossible to manage daily removals and re-installations, thus requiring continuous closure. The overall investment for the 2024 and 2025 trial worksites amounts to 50 million euros.
On 1 September a sequence of operations will begin, starting with the dismantling of the equipment, followed by the installation of a dynamic containment system to protect against asbestos risk and the demolition of part of the concrete vault, preceded by precision milling. This will be followed by water collection, the installation of drainage and waterproofing systems and the reconstruction of the lining, which will involve the use of about 220 prefabricated reinforced concrete segments. Finally, the safety equipment will be reinstalled and, before reopening, the necessary testing will be carried out.
The decision to carry out the work in autumn was agreed with the Italian and French authorities, as during this season light traffic, which accounts for about 75 per cent of all vehicles in transit, is less heavy. Flows will be diverted mainly through the Frejus Tunnel, which will take most of the industrial vehicles, while cars will be split between Frejus, the Great St Bernard and alpine passes. However, some restrictions will complicate these alternative routes. The Petit St Bernard Pass will close on 22 September for works on the French side, while the Great St Bernard Tunnel will be affected by nine night closures between 25 August and 21 October due to works on the Swiss cantonal road. A detailed map of the alternatives is already available on the tunnel website and on the Tmb Mobility app.
The operator has also planned a measure in favour of regular users. All 10 or 20 journey passes valid on 1 September 2025 will be automatically extended by four months, without any action required by customers. The Geie of the Mont Blanc Tunnel has reaffirmed its commitment to respecting the schedule, with the possibility of reopening earlier than 12 December if the works are completed ahead of time.
