The Toronto Transit Commission – not the private sector – will operate four new light-rail lines in the city, the province announced Wednesday.

The decision is a reversal that comes just two weeks after Metrolinx, the province's transportation authority for the Greater Toronto Area, told the TTC in a letter that it intended to ask a private partner to run the Eglinton, Finch and Sheppard LRTs, and the LRT replacement for the Scarborough RT.

The new deal, which comes after months of behind-the-scenes negotiations, means the private sector will design, build, finance and maintain the $8.4-billion LRT network, while the TTC oversees its daily operations.

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The TTC will be responsible for drivers, station operations, security and train control on the new lines, the first of which is scheduled to open in 2019.

"The new infrastructure will remain publicly owned," Transportation Minister Bob Chiarelli said at a joint news conference with officials from Metrolinx and the TTC.

"Most important under this agreement, TTC riders will pay one fare and enjoy seamless, rapid, affordable service no matter where they travel across the system."

The fine print of Metrolinx's arrangement with the TTC has yet to be hammered out.

The two agencies still need to figure out how to set fares, share fare-box revenue and determine how much of a subsidy each will pay to run the lines.

Blindsided by Metrolinx's earlier decision to privatize operations, TTC Chair Karen Stintz warned her agency would not contribute any public money to lines it did not run.

She also flagged safety concerns about having two different operators in charge of different parts of the system during emergencies.

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Bruce McCuaig, the president of Metrolinx, said the letter was not intended to be the "definitive point" in the negotiations.

"I think what was picked up in the past week or so was one moment in time in [the] exchange of one series of letters. That doesn't mean that we we're not having an ongoing dialogue," he said.

Councillor Denzil Minnan-Wong, chairman of council's public works committee, called it a "big mistake" to hand operations over to the TTC instead of the private sector.

"I don't believe that the TTC has a really good track record, especially right now, in terms of operating transit," he said. "I would far more prefer to have a new arrangement and a new operator come in where we could have an operator that actually did run the trains on time."

Toronto's new LRT lines have long been a source of political controversy.

Mayor Rob Ford demanded all the lines be run underground immediately upon taking office. Council later reversed that decision.

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with files from Marcus Gee