On Monday, a worker spotted the crack in the sidewalk of an overpass that crews were resurfacing.
Transport Quebec responded by shutting down Highway 20 eastbound. Officials said the lanes won't be reopened until Wednesday at the earliest.
The closure snarled morning traffic on Tuesday, creating a traffic jam that spanned at least four kilometres.
Workers are expected to demolish the sidewalk as a preventative measure.
Drivers are being told to take a 10 kilometre detour via Saint-Féréol road and Highway 338.
Crews have already been working on the overpass since September.