The latest extension from Sheppard West to Vaughan opened on December 17, 2017, making the line 38.8 kilometres (24.1 mi) long, over five times its original length.

From Mount Dennis in the west to Brentcliffe Road (east of Laird Drive), the line will run almost entirely underground where Eglinton Avenue is generally four to five lanes wide.

From east of Brentcliffe Road to Kennedy station, the line will operate on the surface in a reserved median in the middle of Eglinton Avenue, where the street is at least six lanes wide.

This decision resulted in the destruction of six subway cars and extensive damage to the tunnel and signal lines west of Union station.

Effective November 21, 2021, the TTC introduced OPTO seven days per week on Line 1 between Vaughan Metropolitan Centre and St. George stations.

Between St. George and Finch stations, the TTC continued using two-person train operation[40]: 00:15:38  until the full conversion of the line to OPTO on November 20, 2022.

According to a 2020 survey conducted by the Amalgamated Transit Union Local 113, two-thirds of Torontonians surveyed opposed the TTC's plan to eliminate the train guard on Line 1, and three-quarters of Torontonians disapproved of the fact that the public was not consulted when train guards were removed from Line 4's daily operations in 2016, citing safety concerns, among other issues, as key reasons motivating their response.

[42][43] In 1991, as a result of lawsuits,[citation needed] electronic chimes, in the form of a descending arpeggiated major triad and a flashing pair of orange lights above the doorway, added for the hearing impaired, were tested and gradually introduced system-wide during the 1990s.

Those chimes have become synonymous with the TTC and Toronto in general to the point that the CBC Radio One local afternoon show, Here and Now, includes them in its theme music.

On TTC's Line 2, several symbols of different colours are installed on the station wall for the crew to use as a reference in positioning the train in the platform.

After the doors are opened, the guard is required to stick their head out the cab window to observe passengers boarding and exiting.

An orange triangle[45] installed on the station wall indicates the location where the guard may stop observing the platform and pull their head back into the cab.

In addition, the TTC's Toronto Rocket subway trains provide visible and audible automatic stop announcements.

During such events, the TTC runs "storm trains" overnight along subway lines to keep power rails clear of ice.

The stations along the University Avenue section of Line 1 Yonge–University, in particular, are named entirely for landmarks and public institutions (Museum, Queen's Park, and Osgoode) and major churches[citation needed] (St. Patrick and St. Andrew).

[63] According to a 1991 CBC report, "aesthetics weren't really a priority" on Toronto's subway system, describing stations as "a series of bathrooms without plumbing".

Each station is 'a total art experience where artists have created imaginative environments, uniquely expressing themes of community, location, and heritage' through panoramic landscapes and ceramic wall murals.

"[65] In 2012, the TTC awarded a contract to BAI Communications Canada to design, build and maintain a celular and Wi-Fi system along Toronto subway lines.

[73] In September 2023, the federal government imposed new licence conditions requiring that cellphone and data services be available on the entire subway network by the end of 2026 and that all carriers, including Telus and Bell, were to have access to it.

[76] Rogers and the TTC decided to end TConnect, the free public Wi-Fi service, on December 27, 2024, due to low usage and the cost of upgrading it.

[75][76] Wireless service is available to customers of Rogers, Freedom Mobile, Bell and Telus (including flanker brands of these companies such as Koodo and Virgin Plus).

All subsequent heavy-rail subway cars were manufactured by Bombardier Transportation or one of its predecessors (Montreal Locomotive Works, Hawker Siddeley, and UTDC).

[96]: 30  On October 13, 2022, the TTC issued a request for proposals to construct 480 new subway cars (80 six-car train sets) of a design different from the T1 and Toronto Rocket fleet for delivery between 2027 and 2033.

In conjunction with ATC, stations will have platform-edge doors for safety, also allowing riders to exit and enter trains more quickly.

This was due to delays in planning and construction of the Line 2 extension (which was then projected to open in 2030 at the earliest) along with the increasing difficulty of performing critical maintenance work on the trains.

[111] In 2009, the TTC awarded a contract to Alstom to upgrade the signalling system of the existing section of Line 1, as well as equip its extension into Vaughan, with moving block–based communications-based train control (CBTC) by 2012.

[109] The first section of the "Urbalis 400" ATC system on Line 1 entered revenue service on December 17, 2017, between Sheppard West and Vaughan stations, in conjunction with the opening of the Toronto–York Spadina subway extension (TYSSE) project.

[117] Line 3 Scarborough was equipped with automatic train control from the outset, using the same SelTrac IS system as Vancouver's SkyTrain, meaning it could be operated autonomously.

In addition, there will be scanners within the yellow tactile strips along the platform edge to issue an audio warning if a person steps on it before the train has arrived.

[141] In 2020, a preliminary agreement was signed between the Ontario provincial government and York Region that anticipated the completion of the extension by approximately 2030.