In a city that often seems mired in endless transit debates, there are small but promising signs of momentum on the subway project widely seen as Toronto's top priority.

The regional transit agency Metrolinx is pushing ahead with early work on the long-dreamed-of downtown relief line, new details about federal infrastructure funding this week offered hope for public transit, and TTC chief Andy Byford seized on the Prime Minister's recent visit to make his pitch directly.

"I was the one that raised the downtown relief line," Mr. Byford said on Friday, describing his conversation with Stephen Harper during an unannounced visit on Thursday to a Toronto-area subway project. "He was really interested. He was very understanding of the fact that Toronto only has one primary north-south subway line, and he understood that there is a need to continue to invest in our subway network."

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Although financial commitment to the multibillion-dollar downtown line was not forthcoming, Mr. Byford was encouraged by details about federal infrastructure money that emerged this week. The Building Canada Fund is worth $10-billion, he noted, and 40 per cent is for transit.

"I don't mind where the money comes from, what I do know is Toronto needs more transit," Mr. Byford said after the TTC rolled out its new customer charter, which included a commitment to push other levels of government for funding.

New subway capacity to soak up people going to Toronto's downtown has long been seen as crucial to the city's future.

The Yonge line is increasingly full, and technological improvements will hold the crush at bay only so long. The TTC says that Yonge-Bloor station, the choke point on the system, will be overwhelmed by 2031. Even now, peak-time commuters on parts of the line can be forced to watch several trains go by without being able to board.

The solution is usually seen as a new, roughly U-shaped subway line that would intersect the Bloor-Danforth line at points east and west of the Yonge line and lead into the core.

Both the Liberals and Progressive Conservatives at Queen's Park agree on the urgent need for the line, although they differ on how to pay for it. Transit officials and planning experts typically say it is the obvious next expansion project for the subway system. And even Toronto Mayor Rob Ford, who once said downtown had "enough" subway lines, says the DRL is a priority, although he usually places it after new subways on Sheppard and Finch avenues.

Many details about the line remain to be settled, including the exact route, the extent to which it needs to be tunnelled or can use surface corridors, the final price and how to pay. But work on the complex project has begun. At a Metrolinx board meeting on Friday, staff said public consultation would begin next month. And they cited a long list of tactics – from faster surface routes to fare integration – to help address crowding in the short run.

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"To actually build … is going to be a 10-plus-year project, and we think we shouldn't say that's the only answer and that we have to wait 10 or 12 years to have it done," Metrolinx chair Rob Prichard said after the meeting. "So the key is to find the early inputs, the early outputs, what can we do earlier."