Mayor John Tory's office will release numbers on Tuesday that show his key transit proposal could attract many more riders than he promised during the election campaign – figures that are much higher than a separate study looking at another version of the plan.

The long-awaited preliminary ridership figures for SmartTrack are going to be released at Toronto City Hall, along with a feasibility report into one of the most contentious parts of the proposal. The city numbers, prepared by academics connected to the University of Toronto, are a win for Mr. Tory, who ran for mayor in 2014 on a promise to improve transit.

These numbers are sharply at odds with projections produced internally by the regional transit agency Metrolinx, though. And because the two sets of numbers are based on different versions of the plan, where the ridership ends up will depend in part on how closely the final project echoes the assumptions used by the people running the models.

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The city's figures – using assumptions for ridership modelling that hew to the plan Mr. Tory pitched during the campaign – look ahead to 2031 and show about 77,000 riders per day if trains come every 15 minutes. But that would more than quadruple to about 315,000 a day if the trains run every five minutes. During the campaign, Mr. Tory's team estimated 200,000 daily riders, calling that a conservative figure.

"There appears to be a very significant latent demand for transit service in the corridor that manifests itself once the transit service becomes sufficiently attractive," according to the report. These figures assume a Toronto Transit Commission fare, and the report shows that charging the same as GO Transit would cut the ridership by half to two-thirds.

The unreleased Metrolinx projection, meanwhile, paints a very different picture. It shows daily ridership in the range of 12,000. This assumes a change from heavy to light rail along Eglinton Avenue West, fewer stations, a GO fare and trains every five to 10 minutes.

A Metrolinx spokeswoman said it was premature to discuss its ridership projections.

"Work is under way, but no outcomes have been confirmed," Anne Marie Aikins said in a statement. "Our effort is a collaborative one with the city, and we will not finalize any forecasts in isolation from our discussions with the city."

The city's projections will be explained Tuesday by chief planner Jennifer Keesmaat and deputy city manager John Livey.

The transit proposal was the cornerstone of Mr. Tory's successful run for mayor. He said it would take pressure off the overcrowded subway system, connect people to jobs and "break the back of the city's congestion problems." He said it would cost $8-billion and be ready in seven years.

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Although the final shape of SmartTrack remains to be seen, some elements have been established. It will be run by Metrolinx and involve the same trains used for electrified GO service. A pending integration of fares means it will probably be priced somewhere between the current costs of GO and the TTC.

As reported exclusively in The Globe and Mail, work behind the scenes by transit and city officials suggests that a smaller and cheaper version of the plan – a modest increase over an expansion the province is planning already on its GO rail network, a move to light rail along Eglinton and a phased approach – will eventually be presented to city council.

The changes being considered by staff could have the advantage of lowering significantly the project's price tag, with Metrolinx estimates ranging from $1.9-billion to $3.5-billion for a smaller SmartTrack. A major portion of the cost savings would be switching to LRT along Eglinton, a technically difficult section of the route that is the focus of the feasibility study being released Tuesday.

But even at a lower cost, the spending will need to be justified by potential usage, making the ridership projections crucial to securing political support at council.

SmartTrack began as a promise to build on provincial plans to electrify GO rail and add service. Mr. Tory's proposal included 22 stations, new track laid from the Mount Dennis neighbourhood in western Toronto to the airport area and more frequent service on the GO lines running through the city. He said it would stretch 53 kilometres, from Mississauga to Markham.

Under the new version being worked on behind the scenes, not only would the section in the west end become an LRT, it would go to the airport, instead of near it. The section north of the Kennedy station would be pushed into the future and there would be four or five new stations on the remainder of the route.