The Mont Blanc tunnel connecting France and Italy is now closed for nine weeks and is due to reopen on December 18.
Traffic between France and Italy will therefore have to pass through the Fréjus tunnel.
The long scheduled and overdue maintenance will concentrate on the replacement of the tunnel’s ventilation turbines.
Since workers must take samples from a part of the tunnel's ceiling that contains asbestos, the whole tunnel must remain fully closed for the duration of the work.
Renovation of the ceiling was initially scheduled to take place at the same time as work on the ventilation turbines, however this was postponed until next year following the landslide in Savoie that caused the closure of the Fréjus tunnel in August.
There were concerns that the complete renovation of the tunnel would take too long and lead to disruption of the winter ski season, a possibility that both countries are keen to avoid.
"In accordance with the prefecture of Haute-Savoie, we are committed to meeting the deadline of December 18," Renzo Testolin, president of the Italian region Aosta, told AostaSera.
"This date is crucial in allowing winter traffic to flow normally. If it is possible, we would like to reopen the tunnel before then," he said.
Tunnel passes purchased for the period of the closure are to be extended by three months to compensate for the disruption.
The current closure represents the longest period that the tunnel has been closed since its reopening in 2002 following the fire of March 24, 1999 that claimed 39 lives.