A bomb threat closed the Mercier Bridge for a portion of Friday morning.
Police said the threat turned out to be a hoax.
The bridge reopened at around 8:45 a.m.
In a statement, the Surete du Quebec said it has opened an investigation into who made the bomb threat.
The threat backed up traffic even more than usual on the Mercier, which has been plagued by traffic problems due to construction that has reduced the bridge to one lane of traffic in each direction.
The lane closures are slated to continue until late August, forcing some commuters to adjust.
Marianne Dufour of Kahnawake said she spends about four hours a day getting to and from work. Her employer at the Douglas Hospital in Verdun has given her flexible hours to accommodate for time spent on the bridge
“This morning I left at 5:45,” she said. “Would you believe? Just to come at 7:20? It's very awful every morning.”
The transport ministry is encouraging people to use public transit, though some commuters say it won’t make a difference if they take the bus when only one lane is open.
There is a silver lining, however: A truck ban will take effect next Tuesday, forbidding large trucks and tractor trailers from crossing the bridge during rush hour.