The TTC says planned work to upgrade its ailing infrastructure will require several major subway shutdowns this fall.

The first major closure will take place for three days over the Thanksgiving Weekend, when the Yonge-University-Spadina line will be shut down from Bloor Station to St. George Station.

The upgrades will also necessitate a subway closure from King Station to Osgoode Station during the work week from Oct. 15 to Oct. 18.

One more closure will see the subway shut down from Bloor Station to St. George Station over the weekend of Oct. 19 and Oct. 20.

Shuttle buses will be running to replace regular subway service during those periods and the TTC says it is coordinating the October closures with the city.

While regular maintenance work is carried out overnight when the subway is not operating, the TTC says the signal upgrade work is labour-intensive and requires a longer window of time to complete.

The announcement about the fall upgrades comes on the heels of a major service interruption that delayed thousands of customers Wednesday morning when the train signalling system at Bloor Station failed during the morning commute.

The technical breakdown forced the TTC to bring in shuttle buses along Yonge Street to help move riders to their destinations.

The delays prompted TTC CEO Andy Byford to record a public apology broadcast over the TTC’s announcement system the following day.

“The big issue is that the infrastructure has to be replaced,” TTC spokesperson Brad Ross told CP24 Friday. “By 2018, the entire line will have what’s called automatic train control and that will eliminate the kind of issues we saw on Wednesday with the signal failure.”

Ross said the work that will be carried out in the fall will install the new signalling system on the ‘U’ portion of the Yonge-University-Spadina line. The new system will function as backup until the signal system replacement is completed along the entire line by 2018.

He said the upgrades will cost between $400 million and $800 million and are being funded by both the city and the province.

Ross also said the Bloor-Danforth line – operational since 1966 – is coming to the end of its lifespan and will soon require upgrades as well.

@Josh_F is on Twitter. Remember for instant breaking news follow @cp24 on Twitter.