More than two dozen of the Toronto Transit Commission's aging streetcars have been taken off the road due to extreme cold.

Streetcars on the 511 Bathurst, 502 Downtowner and 503 Kingston Road routes were replaced by buses on Tuesday afternoon and Wednesday morning, as 28 of the vehicles are unable to go into service due to the bitter cold. The City of Toronto remains under an extreme cold weather alert.

"The aging streetcar fleet and related equipment (over 30 years old in some cases) do not respond well to extreme cold," the transit agency said in a statement on Tuesday. "Pneumatic air lines that provide braking, door and windshield wiper operation may have moisture build-up, which can freeze, causing a streetcar to be taken out of service."

The TTC normally operates approximately 200 streetcars during peak-service hours.

Commuters are being warned of longer than normal travel times on the affected routes. The TTC says the 28 streetcars are expected to be out of service at least until Wednesday afternoon.