Toronto's subway extension now 75% complete; 11-metre tunnel unique in Canada
Metrolinx revealed the Scarborough Subway Extension's record-breaking diameter. Riders won't step aboard until around 2030.
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Update — August 06, 2026: Construction has begun on the Lawrence Avenue and McCowan Road station, the second of three planned stops on the Scarborough Subway Extension. The 7.8-kilometre extension features Canada's widest-diameter subway tunnel, a single-bore design carrying train traffic in both directions, with tunnelling work approximately 75 per cent complete as of 2024.
The largest subway tunnel in Canada is now three-quarters of the way to completion. The Scarborough Subway Extension—a 7.8-kilometre, three-stop extension of the TTC's Line 2 Bloor-Danforth—will replace the closed Scarborough RT and carry riders between the current terminus at Kennedy and a new endpoint at Sheppard Avenue and McCowan Road.
Under construction since 2021, the SSE tunnel has reached 75 per cent completion, according to Metrolinx. The tunnel's almost 11-metre diameter is the widest of any subway tunnel in Canada. Both directions of track run in a single-bore tunnel—an uncommon configuration compared to the twin-tunnel method used on most modern transit lines in the city.
The scale is staggering: you could comfortably house a three-storey building inside the tunnel. Managing that width required specialized infrastructure—Metrolinx recently installed a 108-metre-long movable turnout called a California Switch within the tunnel worksite, allowing construction trains to pass using a single track. The temporary system helps "keep materials moving efficiently to the tunnel boring machine as excavation continues," Metrolinx said.
Riders won't see service begin until around 2030. The extension will connect to Scarborough General Hospital. How many new riders or daily commuters the SSE is expected to serve when it opens remains unclear.
At a glance
Where is the Scarborough Subway Extension going?
The Scarborough Subway Extension will run 7.8 kilometres from the current Line 2 terminus at Kennedy Station to a new endpoint at Sheppard Avenue and McCowan Road, serving three new stops and connecting to Scarborough General Hospital.
When will the Scarborough Subway Extension open?
The Scarborough Subway Extension is expected to begin service around 2030.
What's unusual about the tunnel design?
The Scarborough Subway Extension's tunnel is almost 11 metres in diameter—the widest subway tunnel in Canada—and uses a single-bore design with both track directions in one tunnel rather than the twin-tunnel method used on most modern transit lines in Toronto.
