The Extension involves 6.2 km from Downsview Station to Steeles West Station (in Toronto) and 2.5 km from Steeles West Station to Vaughan Corporate Centre Station (in Vaughan). Six new stations will be created on the Spadina Subway Line: Sheppard West, Finch West, York University, Steeles West, Highway 407 Transitway, and Vaughan  Corporate Centre.

AECOM submitted the Environmental Assessment Report, on behalf of the TTC, for the extension of the Spadina Subway to York University. At 6.2 km long, with four new subway stations, this project is the largest undertaking by the TTC since completion of the Sheppard Subway. This project will provide fast and reliable service to the 65,000 students and faculty at York University and represents the first subway project that will extend beyond the municipal boundary of the City of Toronto.