The province is willing to put up the full cost of building a light rail line in Mississauga and Brampton, The Globe and Mail has learned, a commitment that would appear to push far into the future any chance of a relief subway line in downtown Toronto.

‎The regional transit agency Metrolinx will announce on Tuesday it is moving ahead on the suburban LRT project, the cost of which has been pegged at $1.6-billion. The province is going ahead without a funding agreement with the federal government, though the pledge to build the LRT would allow it to apply for federal assistance that could reduce the price tag.

The LRT pledge comes only months after Mississauga ruffled feathers by saying it couldn't contribute anything to the project.

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The 23-kilometre proposed LRT would run from the Port Credit to Brampton GO stations, making a loop around the Mississauga City Centre area.

If Queen's Park's ends up covering the bulk of the cost, it will mean that most of the roughly $16-billion in new provincial transit spending promised over 10 years – the biggest expansion in decades – will be outside Toronto. After a GO rail investment announced Friday and this LRT, there could be little left in the transit funding pot.

The provincial willingness to carry the full cost of this project is in line with light rail pledges made by Queen's Park in years past. But it runs counter to the more recent practice of paying only a third of the capital cost, and expecting the federal and municipal governments to pick up the rest. This sort of cost-sharing is the funding model for the Scarborough subway extension and for Toronto Mayor John Tory's SmartTrack transit plan.‎ The announcement adds to the growing tab for transit that will primarily serve riders outside Toronto.

On Friday, the provincial government said that it would pour $13.5-billion into expanding service on the regional GO rail network. That investment would mean there would be only about $2.5-billion left from the total of about $16-billion earmarked for transit in the Toronto and Hamilton regions.

Asked at that announcement where that huge investment would leave the other projects in the so-called "next wave" of priorities identified by Metrolinx – a list that includes a downtown relief line for Toronto – Minister of Transportation Steven Del Duca said the public would have to wait and see. More news is coming, he said.

If the Mississauga-Brampton LRT ends up being funded by the province, it could soak up most of the money left after Friday's announcement, leaving little for everything else.

This is at odds with the logic behind the next wave of projects, which included a mix of priorities across the Toronto and Hamilton areas, hoping to offer something for as many people as possible and build regional support.

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This list of projects was unveiled late in 2012 by Metrolinx CEO Bruce McCuaig. It included some expansion of GO rail but also a number of other projects.

Only a few months later, then-transportation minister Glen Murray was dressed down by the provincial government for saying that the projects were open to change. His assessment has since proved true, as the province put increasing focus on GO rail to the exclusion of most of the remainder of the next wave.

Insiders have said that the government never really bought into the downtown relief line and kept looking for ways to avoid having to build it. When Mr. Tory proposed piggy-backing his transit proposal onto existing provincial plans to electrify GO, saying it would bring the necessary relief to the overburdened Toronto system, the DRL could be moved down the priority list.