Project Profile: Scarborough Subway Extension (SSE), Toronto

The Scarborough Subway Extension (SSE) is a 7.8-kilometre, three-station expansion of Toronto’s TTC Line 2 Bloor-Danforth, engineered to replace the decommissioned Scarborough RT and provide high-capacity transit to the city’s eastern borough. This project represents a critical infrastructure upgrade, utilizing advanced single-bore tunnelling technology to connect Kennedy Station with a new terminus at Sheppard and McCowan. This profile details the project’s technical specifications, construction status, and strategic objectives as of late 2025.

Technical Specifications

The core engineering component of the SSE is the construction of a 7.8 km twin-track subway in a single, 10.7-metre diameter bored tunnel. This alignment runs from the existing Kennedy Station north to a new terminal at Sheppard Avenue and McCowan Road. The tunnelling is being executed by a custom-built Tunnel Boring Machine (TBM) designed to navigate the specific geotechnical conditions of the region, which include shale and glacial till deposits. The project also involves significant ancillary works, including the construction of eight emergency exit buildings and multiple traction power substations (TPSS) to support train operations. Prior to major excavation, extensive utility relocation for watermains, natural gas lines, and telecommunications infrastructure was required along the entire route to mitigate service disruption.

Key Takeaways

• Infrastructure Replacement: The SSE directly replaces the obsolete and decommissioned Line 3 Scarborough RT, transitioning the corridor from a medium-capacity system to a high-capacity, heavy-rail subway integrated with the city’s primary transit network.
• Economic Catalyst for Scarborough: The project is a major economic driver, projected to support approximately 34,000 jobs within walking distance of the new stations by 2041 and unlock significant transit-oriented development opportunities around Scarborough Centre.
• Enhanced Network Connectivity: By extending Line 2, the SSE creates a seamless “one-seat” ride to downtown Toronto and establishes crucial interchange points with GO Transit, Durham Region Transit, and local bus services, forming a more resilient and integrated regional transportation hub.

Frequently Asked Questions (FAQ)

When will the Scarborough Subway Extension open?

The Scarborough Subway Extension is currently under construction, with major tunnelling underway. The projected completion and opening for service is targeted for the 2029-2030 timeframe, pending construction progress and final commissioning.

Who is building the Scarborough Subway Extension?

The project is being delivered by provincial agencies Metrolinx and Infrastructure Ontario. The primary contract for the advanced tunnelling work was awarded to Strabag, a global construction and technology group. Programme control and technical advisory services are managed by joint ventures involving major engineering firms like Stantec, Jacobs, Gannett Fleming, and IBI Group.