MONTREAL -- The Mount Royal Tunnel will be closing for about three years starting Monday. 

Transit users from Mascouche and Deux-Montagnes – tens of thousands of them – who rely on trains to get to and from Montreal every day will have to use other transit methods, as the closure is necessary for construction related to the new REM track. 

The tunnel was dug during the First World War – construction over the next three years will modernize it. 

Transit users who were upset by the disruption tried to file for a class action lawsuit, but their request was rejected by the Superior Court of Quebec last month.

The closure was originally scheduled for Jan. 6 but was pushed until the spring

"This postponement will not impact the total time the tunnel will be closed or the overall timing for commissioning thanks to an acceleration of work on all branches," CDPQ Infra said in a statement in December. "It will also remove one winter season from the period during which alternative public transportation measures will be implemented."

At the time, the STM said it was set to rent coach buses to ease commutes into the city during the construction.

This report by The Canadian Press was first published May 8, 2020.