The off-ramp from the eastbound Gardiner Expressway to York, Bay and Yonge Streets closed for good on Monday.
City crews will begin demolition of the off-ramp soon and a replacement will be constructed.
Described by Mayor John Tory as the York-Bay-Yonge "Hot Wheels ramp," the structure was officially shut down at 5 a.m.
Motorists are urged to use Jameson Avenue, Spadina Avenue and Jarvis Street ramps to make their way into the downtown core.
"The Spadina off-ramp is being under utilized for the Lake Shore access," said Const. Clint Stibbe of Toronto police's traffic services.
"You need to pay attention at all times, now that the ramp is closed, and the load is going onto the other three ramps."
Stibbe said many motorists forgot about the closure on Monday morning.
"At about 6 o'clock this morning, the Jarvis ramp was already backed up on to the Gardiner Expressway, affecting the eastbound ramp from Rees (Street). We don't normally see that this early in the morning," he said.
Ramp reopening January 2018
The city said the off-ramp will be torn down and replaced with a shorter ramp that will take cars down to Lower Simcoe Street. The replacement ramp is expected to open in January 2018.
The city estimated that 10,000 vehicles used the off-ramp during peak hours.
As part of the ramp work, crews will widen Harbour Street to four lanes between Lower Simcoe Street and Bay Street, to accommodate car traffic and improve access to the waterfront for pedestrians and cyclists, according to a city news release.