Mayoral candidate Rocco Rossi says he'll dig a tunnel to complete the Spadina Expressway. (CBC)

Nearly 40 years later, Toronto mayoral candidate Rocco Rossi, says if he's elected in October he'll complete the Spadina Expressway — underground.

The Spadina Expressway — which exists in part renamed the Allen Road — was one of the most divisive and controversial transportation ideas ever in Toronto.

The idea was to build a six-lane expressway linking Highway 401 in the north to the Gardiner Expressway in the south.

Residents were outraged that their neighbourhoods would be torn up for the new roadway and mounted a campaign that eventually saw the project killed in 1971.

But part of the roadway had already been built, from Highway 401 to Eglinton Avenue West.

On Monday, Rossi said he wants to finish the expressway and if he's elected he'll build a tunnel from Eglinton Avenue West to the Gardiner. That's a distance of just under eight kilometres.

"I am announcing today, that as mayor, I will begin planning and examining with the top engineers in the field, to extend Allen Expressway underground, into downtown Toronto," said Rossi.

But Rossi did not put a figure on how much the tunnel will cost or exactly who will pay for it.

"I will use my executive experience leading businesses and not-for-profit organizations to create a true public-private partnership that will oversee and fund this project," he said.

But Rossi's idea appears to be based on the supposition that he will be elected to a second term.

"By the end of our first term we will have a plan. We will have the funding and we will have shovels in the ground," Rossi said at a mid-morning news conference.