The proposed subway extension in Scarborough does not mesh with the city's broader transit picture and risks stranding local residents by not having enough stops, Toronto's chief planner has warned.

Jennifer Keesmaat called Wednesday's surprise announcement from Ontario Transportation Minister Glen Murray an attempt to "contort a plan" into a set amount of money.

The frank assessment comes as the city grapples with the fallout of Mr. Murray's unexpected announcement that the province would push ahead unilaterally to build a short subway extension into the east end of Toronto.

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The news was greeted with shock at city hall, where TTC chair Karen Stintz was unhappy at being sidelined, and by sniping from Ottawa that Mr. Murray was being "counterproductive." Immediate concerns were raised about the validity of the plan's engineering assumptions, as well as questions about who was in charge of transit planning in the region.

"They asked us for our input, we gave them our input," Ms. Stintz noted on Thursday, referring to a council vote approving a longer subway on another route. "They chose something different."

To these issues can be added the questions raised by Ms. Keesmaat, who has shown a willingness to ruffle feathers since being hired as chief planner in 2012.

"My concern is that we're having a debate here that is very focused, but is not taking into account the need to build out an entire network across the city," she said an interview. "You're planning a network, you change one piece of the network and it has a whole variety of different implications. So the challenge with this exercise is that it's talking about one line, which, you know, I would argue is not really a desirable way to plan transit."

The original plan for the area was to replace the aging rapid-transit line beyond Kennedy subway station with light rail that would run north and intersect with an LRT planned for Sheppard Avenue. But Toronto Mayor Rob Ford and others argued it would be treating Scarborough residents as second class to give them anything but subways.

As the clamour built this summer, the provincial transit agency Metrolinx said it would stop work on the LRT until it had clarity from the city. Council then voted for a subway on a new route, conditional on securing additional funds, which have not materialized. On Wednesday, a clearly frustrated Mr. Murray said the province would revert to the LRT route and build a short subway extension from Kennedy station to Scarborough City Centre. The plan sparked a storm of comment and criticism.

On Thursday, Ms. Keesmaat took particular issue with the number of stations being mooted for the extension. Transit planners generally assume that people will walk to a station from within a radius of 500 metres, meaning that stations, ideally, should be no more than one kilometre apart.

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The map mounted alongside Mr. Murray for his announcement depicted two stops on the 6.4-kilometre route, although he later said that was not necessarily representative of the final number. "The budget considers options for a multiple number of stations," he told CBC radio on Thursday morning.

Mr. Murray's office referred queries about how much this aspect of the project would cost to Metrolinx. A spokeswoman for the transit agency said it was too early to provide breakdowns on the cost or number of stations.

"It wouldn't be serving the people of Scarborough, because a lot of them, they would have a subway going through their community but they wouldn't actually be able to get on it," Ms. Keesmaat said of the proposal as presented.

"We've never had a situation in building transit infrastructure where we haven't gone well over the allotted contingency. So I would caution any kind of recommendation that didn't build in the exact costing of the number of stations. The station is a very expensive part of the infrastructure and I would caution any plan proceeding that didn't very carefully account for an appropriate number of stations, which I would argue should be five, based on the 500-metre radius."

With a report from Elizabeth Church