The decades-old streetcars use pneumatic air lines to operate the brakes and doors. TTC crews purge the lines at night but during the day, moisture in the lines can freeze and prevent the doors from operating. Disabled cars block the way for other streetcars, creating cascading delays.
The TTC is currently sending out 13 buses to replace 502 Downtowner and 503 Kingston streetcars.
Last winter at this time, the same issue caused streetcar service to be interrupted several times, though even more streetcars sidelined due to the temperature.
The city is in the midst of a cold weather snap. With extreme cold, icy winds and a forecast daytime high of just -17 C, Toronto experienced its coldest day of the year on Wednesday.
Environment Canada has issued an extreme cold warning for southern Ontario and at 7:30 a.m. the city's chief medical officer issued an extreme cold weather alert. The city's cold weather alert — which comes after two men died after being found unconscious outside in freezing temperatures — opens warm up centres and more shelter beds available.
With windchill, Toronto may feel as cold as -30 C with winds gusting in the 60 km/h range.