Tunnels are either square or round, depending on the method of their construction: Square tunnels were built with the cut and cover method of digging trenches down from the surface, constructing the tunnel structure, and then backfilling. Round tunnels are bored using a tunnel boring machine. The cut and cover technique was used extensively on the oldest portions of the subway system, while newer sections were predominantly or, in the case of the Toronto-York Spadina Subway Extension, which opened in 2017, entirely bored. Some sections of track run on the surface, the most notable on the heavy rail subway system being the stretch of Line 1 Yonge–University in the median of Allen Road. However, the light metro Line 3 is a surface or elevated route for nearly its entire length.
Diamond crossovers
are X-shaped track assemblies that are used, particularly at terminal stations, to allow trains to reverse direction and enter the opposite track. They also exist outside some through stations where they are often used to short turn trains. A single-crossover just east of Union Station is what remains of the former diamond-crossover, which was used when the station marked the southern terminus of the original line. A few crossover tracks that were built as part of the original subway system have since been removed; their locations are marked by tunnel sections where there are no central pillars between tracks. Crossovers are found in the vicinity of the following stations:
Centre tracks allow a train to enter from either end into a third set of tracks, longer than the length of a standard train, between the two service tracks. Trains can either layover or short turn there, allowing other trains to pass them by, or reverse direction from this position with minimal interference with through trains compared to crossovers, which requires the reversal to take place on station platforms. Sometimes, regular trains are diverted into centre tracks when there is track maintenance on one of the service tracks. Pocket tracks are a variation on the centre track, accessible only from one end. Storage/centre tracks are found in the vicinity of the following stations:
Yonge–University line
*North of Finch West
*South of
*North of
*South of
*Between and Union
*North of Eglinton
*South of
*North of Finch
Bloor–Danforth line
*East of Islington
*East of
*West of
Scarborough line
*There are no centre tracks or storage tracks on Line 3.
Sheppard line
*There are no centre tracks or storage tracks on Line 4.
Other track features
Track configurations become more complicated where lines meet, and at the entrances to subway yards. Tracks usually continue for roughly the length of a train beyond the last station on a line; these are known as tail tracks. The only exception to this is at Don Mills Station, where the tail tracks are less than two cars in length. This is likely because storage capacity is available at Sheppard–Yonge, which can store enough trains to service the line. The tail track structures at some terminal or former terminal stations also have, or have provisions for, a third tail track. Finch Station has such a triple configuration, Vaughan Metropolitan Centre Station is a terminal station with an trackless tunnel section for installation of a potential third tail track, and Sheppard West Station was a formal terminal also built with a trackless third tunnel north of it, which could now accommodate a future standard pocket track. Other track features that exist include the following: The Bloor Wye was used for interlining in 1966:
North of Museum station, the tracks split, with the Line 1 mainline leading west to St. George station, and the other east to Bay lower.
The eastbound track from Bay lower joins the Bloor–Danforth line just before Yonge station while the westbound track from Bay lower turns and meets the southbound track just north of Museum station.
The eastbound tracks approaching St. George Station from Spadina on the Bloor-Danforth line split, with one heading for St. George lower and the other heading for St. George upper.
The westbound track headed to Spadina Station west of St. George upper now includes a switch that allows trains to run to Spadina Station on the Spadina line, which was built more than a decade after the interlining trial was completed.
An access track leading west to Wilson Yard south of Sheppard West station from the southbound direction, defaulting from the crossover track section leading to/from the station's northbound platform. Trains needing to access the yard from the south must reverse at the station or access it from the crossover north of Wilson station.
A maintenance track, accessible from the eastbound track on the Bloor–Danforth line, just west of Warden Station. Trains must run in reverse to access this siding
The Sheppard Wye includes the following features:
Northbound Yonge line to eastbound Sheppard line: track switch on the Yonge Line that meets the Sheppard line east of Sheppard–Yonge station
Westbound Sheppard line to southbound Yonge line: west of Sheppard–Yonge station on the Sheppard line storage tracks and switches allow trains to proceed from east to south connecting with the southbound Yonge line just south of Sheppard–Yonge station
Each of the three subway yards have different features that join them to the mainline. Subway operators generally get their train at a point where the yard meets the main line, at the Greenwood Portal, the Davisville Buildup, or the Wilson Hostler depending on the home yard. Tracking from Union to Eglinton stations is aging and there is a proposal to upgrade trackbed from Eglinton to St. Clair stations to improve service, but could result in service interruptions.
