The simmering battle over how best to expand Toronto's subway network grew more contentious and complicated after a Metrolinx board meeting Thursday.

During the meeting, planners for the provincial transit agency said the downtown relief line must open before Line 1 is extended farther north into York Region.

The two projects are both considered integral to Metrolinx's 2041 Regional Transportation Plan. However, there are disagreements between experts and municipalities about which line should take priority.

The long-discussed downtown relief line — called the Relief Line South by Metrolinx — would run south from Pape Station and terminate at either King or Queen Stations. The proposed Yonge North Subway Extension would run from Finch Station to Richmond Hill Centre, just north of Highway 407.

A proposed extension of the relief line would alsoconnect Pape Station to Don Mills Station on Line 4.

Metrolinx says both portions of the relief line and the Yonge subway extension are 'priority projects,' but it's unlikely they can all open simultaneously. (Metrolinx)

Markham Mayor Frank Scarpitti, also the chair of the York Region Rapid Transit Corporation, attended the meeting to push back against claims that the relief line must open first. He has been advocating for construction on the Yonge extension to begin as soon as possible.

"When I hear data being presented that gives momentum to the fact that the Yonge subway shouldn't start and get underway, you're going to hear from us in York Region," he said. "The Yonge subway extension is not going to take a back seat to any other project in the GTA."

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