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Claudia Néron, a spokeswoman for Pulsar, the operator of the REM, said there was a problem with the trains that triggered safety measures.

"The crews identified a problem with snow infiltration on wheel components, which triggers protective system measures and therefore the automatic shutdown of the trains," Néron said in an emailed statement. 

She said a solution has been identified and will be gradually implemented across the entire fleet of trains in the coming days.

The latest incident is the 17th time the network has seen an interruption of more than 20 minutes since the new branch of the light rail serving Montreal and cities to the north first opened in November.

Néron noted that six of the disruptions were attributed to external factors: significant ice accumulation on Dec. 29, two intrusions onto the tracks, alarm activations by passengers, and a truck that collided with an overpass on Nov. 18. 

"Generally, these disruptions last less than an hour on a 20-hour service day," Néron said.

The new 30-kilometre extension of the REM opened on Nov. 17 and travels northwest from Central Station, through a tunnel under Mount Royal linking the campuses of McGill University and Université de Montréal, before it continues along the north end of the island and on to Laval, Que., and the Deux-Montagnes station.

The first five stations linking Brossard to Central Station opened in 2023.

Néron said the operator apologized for the service interruption, which occurred as several days of cold weather settle in to the Montreal area. 

On Tuesday, the system started slowing down around 8 a.m. and went completely out of service for about one hour before it was up and running at full capacity just before 10 a.m.

Shuttle buses were deployed, causing lengthy lineups at some stations for people seeking to get to downtown.

"Winter presents additional challenges, but our teams always find solutions," Néron said. "Operating on a network that now spans 50 kilometres reveals new issues for which we are working to deploy upgrades."

Two branches are yet to be opened. One branch to Montreal's West Island suburbs is expected by spring, while a branch to Montréal Trudeau International Airport is expected at some point in 2027. 

Earlier this month, a REM train used the branch leading to the airport for the first time and work in the tunnel leading to the airport station is progressing, with the station nearing completion.

Once complete, the network will have 26 stations across 67 km.

This report by ºÃÉ«tvwas first published Jan. 20, 2026.