Badly needed upgrades will grind subway service to a halt in the heart of downtown for nine consecutive days in October, an unprecedented closure that stands to affect hundreds of thousands of commuters.

While the TTC replaces the outdated, increasingly unreliable signalling system that caused a major disruption this week, there will be no service on the Yonge-University-Spadina line between Osgoode and King stations, from Oct. 12 to 20.

The entire downtown “U,” from St. George to Bloor stations, will be closed during the two weekends that bookend the nine-day period, the first of which is Thanksgiving weekend.

TTC spokesman Brad Ross said it will take three days to do the first phase of the work, which necessitates replacing the decades-old hardware on the entire loop. The TTC chose a long weekend to minimize the disturbance, he said.

But commuters in the downtown core will feel the pain when a significant portion of the subway — which includes bustling Union station — remains closed during the week, a first in the history of the TTC.

Ross said the TTC will use shuttle buses during subway closures, and rely on uniformed personnel to direct foot traffic at stations and in the underground PATH system. Details of the transportation plan, however, have yet to be finalized, he said.

“We’ll get people around. It will be an inconvenience but when all this is said and done the benefit will be a modern signalling system,” he said. “You have to bite the bullet.”

A new $500-million computerized system on the Yonge-University-Spadina line is expected to be in place by 2018.

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