Open this photo in gallery Commuters using the TTC subway in Toronto Mar. 26, 2012. Moe Doiron/The Globe and Mail

A half-billion-dollar project that will help relieve crowding on Toronto’s busiest subway line will take up to two extra years and an unknown amount of additional money to complete, The Globe and Mail has learned.

According to multiple people familiar with the project, a decade-long effort to install a modern signalling system that would allow more frequent subway service on the Yonge-University-Spadina line is no longer expected to be finished in 2019, the date that was decided on when the project was overhauled in 2015. The sources were granted anonymity because they were not authorized to discuss the matter.

The $563-million project to install automatic train control (ATC) in the subway tunnels of Line 1 has been in the works since 2008. It involves replacing a signalling system that, in some cases, dates to when the Toronto Transit Commission subway first opened more than 60 years ago.

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Shelagh Pizey-Allen, executive director of the transit advocacy group TTC Riders, said that the new signalling system is a critical measure to help alleviate crowding in the years before a relief line can be built.

“We hear stories of people trying to board the Yonge line who wait for multiple subways to go by, and they can’t get on because it’s so crowded,” she said. “So it’s really important that automatic train control moves ahead as fast as possible."

The signal system being replaced is increasingly unreliable and prone to breakdown, routinely causing headaches for passengers caught up in the resultant delays. But its impact goes deeper. With the old signalling system, operators were forced to maintain substantial buffers between trains. With ATC’s computerized system, trains would be able to operate more closely together, allowing the TTC to run more of them.

The TTC normally schedules 25.5 trains an hour at its busiest and managed Wednesday, for only the second time, to boost that to 29. With ATC technology, 30 or more trains per hour could be reliably expected, along with a greater consistency that could smooth out frustrations in how often trains arrive.

The ATC system was supposed to be installed by 2019 and operational the following year.

TTC spokesman Stuart Green said the reasons for the ATC delay, along with details on additional costs and a new timeline, would be revealed when an independent review of the project goes to the board next year.

“Is it going to going to take longer than originally planned? Yes,” Mr. Green said. “Is it going to cost more? Yes. How much longer and how much more, I don’t know at this point.”

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According to people familiar with the project, the delay probably ranges from one to two years. The final timeline is likely to depend on how aggressively the work – which requires shutting down sections of the subway – is pursued and how much money politicians are willing to spend.

“The mayor has made it clear to the TTC that as soon as the review is finished he expects to see a plan to get this project completed before any additional costs are incurred,” Don Peat, a spokesman for Toronto Mayor John Tory said in an e-mail.

The external review of the project was ordered in July by the TTC, which said at the time that this should not be construed to mean there were problems with the project.

The third-party look was to determine whether the agency has enough trains and a robust enough ventilation system and power supply to realize the full benefits of the new signal system. It was also to look at whether the 2019 target for full ATC installation remained realistic.

That review has not been made public and the agency has not previously acknowledged that the project would not be finished on time.

Installing subway signal systems can be incredibly complex and delays have cropped up in other cities. The recently announced postponement in opening the new Crossrail subway line in London was attributed in part to problems with the signals. Replacing New York’s antiquated signal system is expected to cost up to US$15-billion and take up to 15 years.

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Among the issues that have emerged in Toronto was that work to install ATC around the Wilson subway yard proved more complex than anticipated. And according to two sources, the agency has decided to be less aggressive about scheduling ATC work in Toronto’s downtown core.

The original plan was to resignal as a package the entire southern U of the line, which would have forced regular shutdowns of the section of tunnel from Dupont station around to the Bloor-Yonge interchange.

This work will instead be done in three separate sections, starting with Dupont to St. Patrick stations, which will be more manageable and also have the benefit of helping minimize inconvenience to passengers.