New analysis is showing how much two of Toronto Mayor John Tory's key transit projects risk competing with each other for riders.

Included in a voluminous release of transit planning reports late Thursday, the finding that SmartTrack could push Scarborough subway ridership below 10,000 per hour is likely to renew questions about the viability of having the two lines operate so close together.

Mr. Tory ran on a promise to extend the Bloor-Danforth subway into Scarborough and also on the proposal he dubbed SmartTrack – a sort of local service added onto the existing GO rail network, including through Scarborough, with 22 stops.

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While campaigning, Mr. Tory often answered questions about his transit proposals by saying he was determined to make them happen. And he brushed off concerns about the two lines competing by saying that he didn't talk to anyone who believed the city was building too much transit. In Scarborough, though, transit planners were alarmed enough to study a broad range of possible alignments for the subway extension, even considering taking it well off the direct route to move it away from Smart Track.

The impact the lines would have on each other is laid bare in the new reports.

"Extending the Bloor-Danforth subway line into Scarborough is an important addition to our transit network and will provide critical transit for Scarborough," mayoral spokeswoman Amanda Galbraith said in a statement. "Ridership numbers are always lowest at the ends of the line, but that doesn't mean that each region of our city should not be served by high-speed transit."

Both Chief Planner Jennifer Keesmaat and Mr. Tory have stressed to reporters in recent weeks that ridership is not the only factor when making transit decisions.

"Of course ridership projections are not the only factor, but they are a core indicator that has been used time and time and time again to provide a rationale for projects," countered midtown Councillor Josh Matlow Thursday evening. "In the specific Scarborough debate, I remember [ridership] being a critical factor."

Mr. Matlow said he did not want to comment directly on the reports until he had had time to read them.

The new reports also included a recommendation from city staff for pared-down versions of SmartTrack. They are urging Metrolinx, the regional transit agency, to consider options that serve 11 existing stations, and between four and eight new ones.

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The new transit ridership figures show that, according to modelling done for the city by researchers at the University of Toronto, the three– or four-stop Scarborough subway extension Mr. Tory campaigned on would have a peak usage of 13,700 to 17,700 people per hour per direction. That is in line with an earlier projection, but the figure drops sharply when the mayor's SmartTrack proposal is added to the mix.

With SmartTrack running trains at 15-minute intervals, the peak number of passengers using the Scarborough extension goes down to 12,600. And with it running every five minutes – which earlier city reports have suggested would be necessary – Scarborough peak ridership goes down to 9,800.

The lowest figure from the latest report is barely more than the 9,500 people city staff projected years ago. That figure was considered marginal for a subway and was later replaced by projection for 14,000 riders, which made the case for a subway stronger but attracted accusations of fiddling the numbers.

These latest ridership projections are not definitive, though.

Since the campaign, a new proposal for a one-stop subway extension has emerged – with an estimated price of $2.5-billion. Changing to that plan would have an effect on the numbers: Fewer stops would mean a faster run by the train, which could attract more passengers, but there would not be as many places for them to board. More modelling work will be needed on this new proposal.

In the reports out Thursday, city staff said that more work was needed to assess demand on a whole series of transit proposals.

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"This work will further assess the network impacts of transit lines [in the report], as well as other potential network additions," they write. "Appropriate sequencing of the range of projects being considered for the transit network will be better understood through this modelling work and will inform the phasing of the possible future transit networks."