TTC chair Maria Augimeri says construction delays at a station on the Spadina subway extension could force the transit operator to limit service on the six-stop line so it can open as planned in 2016.

But TTC CEO Andy Byford said he is still looking for ways to accelerate construction over the remaining two years to prevent that, and is assembling a four-member panel of international experts to advise him on options. The names of the members will be announced as early as Thursday, he said.

"Before I admit defeat, I want to make sure I have left no stone unturned," Mr. Byford said on Wednesday.

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The expert panel will report to Mr. Byford, and is expected to work quickly to prepare its findings by the end of the month. The panel will be made up of experts in the field and will work independently under terms of reference drawn up by Mr. Byford.

Their recommendations are expected to be presented to the TTC commission at its first meeting of the term in December – giving whoever mayor-elect John Tory picks as TTC chair a crucial decision to make right away.

Ms. Augimeri, who became TTC chair earlier this year when Karen Stintz gave up the post to run for mayor, said problems at Pioneer Village Station – on Steeles Avenue, east of Jane Street – are delaying work on the subway extension, which already is behind schedule. As a result, she said the TTC is considering two temporary options: turn trains back at York University or bypass the Pioneer Village station, a move that would allow service to continue to the northern end of the line at Vaughan Metropolitan Centre.

Mr. Byford said he does not want to speculate on possible options until he hears from the experts. A "phased opening" of new lines has been used by other transit authorities, he said, but could present challenges in areas such as signalling and turning trains around.

"People can speculate. I'm the CEO. The official line from me is I wouldn't rule anything out, but I'm not yet making a call," he said. "Right now, that's not officially on the table."

He added that it would be wrong to say Pioneer Village Station is the only one to have problems, noting construction delays and "challenges" at the York University and Vaughan stops as well.

Despite the delays, Mr. Byford stressed that work on tunnelling is complete, track is being laid and most stations are "beginning to look like stations."

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The TTC is the project manager for the $2.5-billion subway extension, which is being funded by the City of Toronto, York Region, the province and federal government.