Italian highway company ANAS said the closure of the Strada della Maddalena was a safety precaution after fires devastated the area between Pietraporzio and Sambuco.
Firefighters on Monday continued to battle the wildfires which have swept through the northern region of Piedmont over the past week.
The situation remains critical in the Susa Valley, while forests and mountains are ablaze in the province of Cuneo and in the Canavese area near Turin.
A suspected arsonist was on Sunday detained in the province of Biella, and will be dealt with accordingly in the coming days.
Hundreds of locals have been evacuated from their homes because of the fires, including residents of a nursing home for the elderly.
Blazes have also broken out in Lombardy.
With ANSA
