Ottawa's Confederation Line experienced several serious problems during the biggest snowfall of the season this weekend, from tripped switches to jammed doors to smoke filling the tunnel.

The most significant delay for riders occurred around 6:30 p.m. Saturday — only a few hours after the snow began falling — when track switches were "disturbed" at the eastern end of the Confederation Line, triggering replacement bus service for two hours.

OC Transpo tweeted about the delay at the time, and on Sunday morning emailed CBC News a statement explaining that "snow interfered with the normal operation of a switch at Blair station."

The email, attributed to transit operations director Troy Charter, explained safety sensors that are supposed to detect whether people are on the tracks were being activated by snow, and could cause trains to come to a sudden halt. To get around this problem, train operators were instructed to move slowly, which would have contributed to the delays for customers.

A persistent problem

Another switch issue caused the Confederation Line to shut down on Sunday evening, again between Hurdman and Blair. This time, according to OC Transpo's Twitter feed, replacement bus service lasted 40 minutes.

Switch problems are among the four main issues that have been plaguing the LRT system, along with jamming doors and two separate computer problems.

City officials have known about the potential problem posed by snow on the switches for some time.

Fibreglass switch covers installed by Rideau Transit Group (RTG) to prevent snow buildup have actually caused some recent delays, and have since been removed along the line. The city has urged RTG to post extra staff on the ground this winter, especially at those switches.

According to Charter, the maintenance arm of RTG "did have staff at various points," but that the oversight didn't appear to be enough to prevent the switch issues.

Door, smoke issue not reported

There were other issues on the Confederation Line this weekend that were not made public, CBC has learned.

On Sunday morning, a train was disabled at Tunney's Pasture station, shutting down service for a while. Around midday, the doors on a train at Hurdman station failed to open, and customers were unable to board or exit the train. It's unclear how long this problem lasted.

Far more concerning was the presence of smoke on the line. According to social media, smoke filled part of the tunnel shortly after 10 a.m. on Sunday. An internal incident report shown to CBC indicated the smoke and a burning smell were caused by a "wheel flat" — a wheel that has ceased turning and is grinding against the track.

Charter confirmed reports of the smoke to CBC, and said the issue is being investigated.

According to a CBC source, another train was removed from Blair station Monday morning after reports of a burning smell and "train slippage."

OC Transpo said in a statement on Monday afternoon that the Confederation Line is down to 10 trains from "the required 13" because of a series of mechanical issues, including the problems with air compressors and wheel issues.

As well, the train that pulled down 80 metres of electric cable last Thursday is being inspected to try to figure out the cause of the alarming incident.