Built 60 years ago, used daily by thousands of vehicles, this two-way structure, 11,6 km long, is at a stage where one-off repairs are no longer enough: "we have chosen to make more important, more substantial work to give a second life to this tunnel", explains Grégory Schwarshaupt, deputy director of the French concession company Autoroutes et Tunnel du Mont-Blanc (ATMB).
It is about its "sustainability in the long term", he explained to AFP.
The long closing periods will be a "first" for the tunnel since it reopened in 2002 after the fire that ravaged it on March 24, 1999, costing the lives of 39 people. The operators, who are simultaneously carrying out renovation work on part of the slab, have so far always managed to stick to night closures, apart from a three-week period in the fall of 2022.
At the time, leaks in the Italian press on potential shutdown scenarios had caused serious concern in Italian business circles, with some fearing that they would "bring the country's economy to its knees".
In France, elected officials are worried about a risk of increased pollution in the Maurienne valley, where traffic could be transferred via the Fréjus tunnel, another important Franco-Italian axis.
Tight and poorly ventilated, the Arve valley, which leads to the Mont-Blanc tunnel, regularly experiences episodes of air pollution, linked among other things to road traffic and its nitrogen dioxide emissions.
The Mont-Blanc tunnel sees around 1.700 heavy goods vehicles pass through the year, while light vehicle traffic averages 3.600 cars/day, with peaks of more than 6.000 in August and troughs in autumn.
The first two construction phases, described as "experimental", should allow the repair of the vault on four sections totaling 1.200 meters, or approximately 10% of the total length, and to develop the most efficient schedule possible. for the remaining 90%, which will also have to be renovated in the following years.
“Not much margin”
The closure will take effect on September 4, 2023, the day after the end of the Ultra-trail du Mont-Blanc (UTMB) events, a great tourist and sporting mass on both sides of the border. End scheduled for December 18, shortly before the Christmas holidays. "We don't have a lot of room" between these two meetings, admits the deputy director.
The first test site will allow the renovation of 600 meters of vault in two places. If its results are positive, an additional 600 meters will be renovated in 2024. These first two phases have been budgeted at 50 million euros, supported equally by the French (ATMB) and Italian (SITMB) concession companies.
For the rest, "everything remains open", underlines Mr. Schwarshaupt, who says "understand the expectation" of regional players, particularly in the tourism sector, and transporters. "The sooner we can communicate, explain how the rest of this project will unfold, the better it is for everyone. It will not be before the end of 2024", he explains.
Some 92% of the goods circulating between France and Italy pass by road, according to the Alpine Territories Agency, i.e. 3 million heavy goods vehicles and 43 million tonnes (Mt) on all the roads in the Alps.
According to Mr. Schwarshaupt, the data collected during the three weeks of closure in the fall of 2022 saw a "90%" postponement of heavy goods vehicle traffic to Fréjus. As for light vehicles, 30% went to Fréjus, 40% to the Grand Saint-Bernard tunnel and 20 to 25% had "disappeared".
Six things to know about the Mont-Blanc tunnel
Road traffic represents about 1.700 heavy trucks per day, while light vehicle traffic averages 3.600 cars per day, with peaks of more than 6.000 in August. That is about two million passages per year, according to figures from the operator ATMB.
The wait at the entrance can be long, especially in summer, because the number of vehicles is fixed in the tunnel: one car every eight seconds, or a gap of 150 meters, regulated by barriers. This is called "pacing". Two coaches cannot follow each other directly, to avoid saturation of the emergency shelters, with a capacity of around forty people, in the event of an emergency. The refrigerated trucks, 5 cm wider than the others, must pass in a convoy of seven, accompanied by service vehicles.
"A before and an after"
The dramatic fire of 1999, which claimed the lives of 39 people and could only be extinguished after 53 hours of fighting, was a turning point in terms of safety in tunnels. The first investigation report after the disaster pointed to a damning series of malfunctions. "There was a before and after in all the tunnels of France, Europe, around the world", underlines Sandra Ziggiotto, head of service for the managing company. Since 2013, the 70 professional firefighters in the tunnel have been equipped with tailor-made trucks.
The structure is equipped with 120 cameras, to which are added those located in each of the 37 secure shelters along the route and 3.860 temperature sensors. In total, the structure has 45.000 control points, which can automatically detect various types of incidents (slowdown of a vehicle, presence of a pedestrian or an animal, object on the road) and alert the control room.
In the event of an emergency, evacuation on foot is via a ventilation shaft located below the roadway. The narrow tunnel, accessible from the emergency shelters, allows the circulation of a small electric vehicle intended to evacuate the wounded. To avoid any confusion, arrows indicate whether you are heading towards France or Italy.
Picnic or baby break
Despite abundant signage in several languages on what is or is not allowed in the tunnel, some users make mistakes. It is quite common for a car to attempt an overtaking, which is totally prohibited. This leads to a fine as soon as it leaves the tunnel, with a different amount in France and Italy.
Some users are also called to order for having parked in the shelters to have lunch, change a baby or say their prayers. Among the most unusual cases, that of a man abandoned in the tunnel with his suitcase by his wife after an argument. "We have everything!" Comment the tunnel managers.