Tunnelling began in January, 2023 at the north end of the extension at Sheppard Avenue East and McCowan Road. On a former car dealership parking lot, excavation opened a launch shaft for the gargantuan, German-manufactured, 10.7-metre-wide tunnel boring machine (TBM) dubbed Diggy Scardust, tasked with constructing the majority of the SSE’s tunnel.
The TBM launch shaft at the northeast corner of McCowan Road and Sheppard Avenue East shortly before the start of Diggy Scardust’s southward journey, image via Metrolinx
The launch of the 6.9 kilometre journey featured the largest TBM ever used for a Canadian subway project. Unlike every other TTC subway tunnel, including the ones for Ontario Line 3, which use twin machines to dig separate tunnels for each set of tracks, the SSE will house both tracks within this single, massive bore.
The tunnel boring machine (TBM) being used to excavate the Scarborough Subway Extension’s tunnel – dubbed ‘Diggy Scardust’, image via Metrolinx
Starting 28 metres below the surface, the TBM has remained deep underground as it has moved south beneath McCowan Road to avoid the ravines and riverbeds along its route. Shortly to follow the path of Danforth Road southwesterly, after turning west along Eglinton Avenue East, Diggy Scardust will end its journey at an extraction shaft at the intersection with Midland Avenue, roughly 400 metres east of Kennedy station, where the tail tracks of the existing Line 2 end.
Excavators dig out an extraction shaft for the tunnel boring machine at Eglinton Avenue East and Midland Avenue in June, 2025, image via Metrolinx
In the more than three years since work began, tunnelling has not always progressed smoothly, with a months-long halt occurring near Highway 401, starting in late 2024. Metrolinx initially refused to release details about these issues but was forced to publicize the TBM’s breakdown following a freedom of information request filed and released by the Ontario NDP.
Looking west over Highway 401 from the McCowan Overpass, image via Wikimedia user Eja2k at https://commons.wikimedia.org/wiki/File:401atMcCowan.JPG
Despite that setback, the TBM resumed its progress and has averaged roughly 9 metres of excavation daily since September, 2025. In a social media post this February, Metrolinx CEO Michael Lindsay shared that the machine was then just north of McCowan Road and Lawrence Avenue East, the future site of Lawrence-McCowan station.
Location of the SSE TBM as of February 2026, image via Metrolinx
Lindsay also shared that tunnelling has reached speeds of up to 20 metres per day lately, likely making up for some of the time lost during the significant delays in 2024 and 2025. Although Metrolinx has not released an updated timeline for completing the tunnel, the recent average speed suggests the machine could reach the extraction shaft in approximately a year’s time.
Route of the Danforth Line 2 extension through Scarborough, image via Metrolinx
UrbanToronto will continue to follow progress on this development, but in the meantime, you can learn more about it from our Database files, linked below. If you’d like, you can join in on the conversation in the associated Scarborough Subway Extension Forum thread, or leave a comment in the space provided on this page.
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