Yesterday the TTC formally released a Request for Proposal (RFP) for tunnel design work of the Relief Line South. More specifically, the RFP is to "complete the Concept Design Report and Preliminary Design and Engineering for the Tunnels and associated facilities for the RLS, together with a cost estimate and project delivery schedule, to 30% design completion." This RFP marks a substantial step forward in the detailed design work for the Relief Line, which is tentatively scheduled to begin construction in 2025 and be complete by 2031. The RFP is scheduled to close on December 15th, with a winning proponent likely announced shortly afterwards.

The approved alignment of the Relief Line South, image courtesy of the City of Toronto

For planning and design purposes the Relief Line has been divided into two segments: The Relief Line South, which runs from Osgoode Station to Pape Station, and the Relief Line North, which will run north from Pape Station, possibly under Don Mills Rd (though the alignment is far less refined). The Relief Line South is being spearheaded by the TTC, while the Relief Line North is primarily a Metrolinx project. The Relief Line South is approximately 6km in length, while the Relief Line North's length depends on what alignment and terminus is ultimately chosen.

The City's Transit Master Plan, with the Relief Line North rough alignment in faded pink, image courtesy of the City of Toronto

The planning and design work for the Relief Line is being funded primarily through a $150 million funding commitment from the Provincial and Federal governments. To date however, there have been no hard commitments for construction funding from any level of government, though the City of Toronto and Metrolinx continue to push the project forward in anticipation of a multi-government funding commitment in the coming years.

The Relief Line South will feature additions/improvements to three existing stations (Osgoode, Queen, Pape), and will add five new stations to the network (at Sherbourne, Sumach, Broadview, Carlaw, and Gerrard streets). Given that some of these streets already have eponymous subway stations on them, the final names of the stations along the line will likely be adjusted in order to comply with the TTC's and Metrolinx's station naming policies. The station at Broadview in particular is likely to be changed to East Harbour, to coincide with the future GO RER/SmartTrack station that will underpin the East Harbour development project at the former Unilever site.

Comparison of the depths of the Bloor-Danforth, Sheppard, and Relief Line tunnels, image courtesy of the City of Toronto

One new piece of information contained in this RFP is that the TTC is open to the possibility of using "a combination of twin-bored, single or mined tunnels". Single-bored or mined tunnels would be a departure from how subways have typically been built in Toronto. The original Yonge Subway (Union to Eglinton), and the majority of the Bloor-Danforth Subway were built using cut-and-cover construction, whereby a trench is dug (cut) under or beside the street, and then decked over (cover) to form a subway tunnel. More recent subway projects such as the Sheppard Subway, Toronto-York Spadina Subway Extension, and Eglinton Crosstown LRT have been/are being built primarily using twin-bored tunnels via Tunnel Boring Machine (TBM). Single-bored tunnelling was recently used in Montreal's Orange Line extension to Laval, while mining operations recently completed on Ottawa's Confederation Line LRT tunnel.

Roadheader advances in mining Ottawa's Confederation Line LRT tunnel, image courtesy of ConfederationLine.ca

Following this RFP announcement, the next piece of news on the Relief Line is likely to come from Metrolinx's preparatory work on the Relief Line North, which should be released in the relatively near future. UrbanToronto is keeping a close eye on this crucial transit project, and will update you as soon as new information becomes available. In the meantime, you can join the discussion on the Relief Line in our forum thread, or by leaving a comment in the space below.