It's the latest issue that Chow has flagged with SmartTrack, the plan Tory has made the centrepiece of his mayoral platform.
Tory's proposal, which was unveiled in May and has an estimated $8-billion price tag, would seek to establish a 53-kilometre, 22-stop rail network that would operate in part on existing GO Transit tracks and would extend beyond the formal boundary of Toronto. One of those stops would be at Union Station.
Tory has argued SmartTrack will improve transit within a few years, on a shorter timeframe than it will take to build a subway.
Chow has previously questioned how SmartTrack will be paid for, how it will be built without tunnelling and how it can make a turn in Toronto's Mount Dennis neighbourhood without demolishing some existing buildings.
On Wednesday morning, Chow questioned how SmartTrack will be able to find space for scores of trains on the tracks at Union Station that she said will be nearly at capacity by the time Tory's plan could be made a reality.
Chow said that through GO Transit and Via Rail, there are currently some 400 train movements through Union Station each day.
That number is expected to double after the Union Pearson Express comes into service and when GO Transit moves ahead with a planned service expansion, she said.
"All of that combined will have 900 trains … and the capacity here at this site is 929 trains per day, which means that there is no room for John Tory's 150 trains a day," Chow said.
In an email, Chow's campaign explained that their estimation of 150 trains is based on the fact that four trains would move through Union Station in a single hour, in both directions. Eight trains per hour, for a 19-hour period — 6 a.m. through 1 a.m. — would involve approximately 150 train movements over the course of the day.
Chow said that leads to questions about what options are available to give those SmartTrack trains space to operate.
What those options are, "we don't know," Chow said, suggesting that tunnelling would be one possibility, though that would be "very expensive."
Tory released a statement Wednesday, defending his SmartTrack plan and suggesting that Chow is not listening to the transit experts she claims to.
"Once again, Ms. Chow has sought to poke a hole in SmartTrack. And once again, nothing has come of it. Renowned transit experts are saying this proposal rates 'an A-plus'," Tory said in the statement posted on his campaign website.