The final stage of Adelaide’s $80 million tram extension is progressing well despite workers sweltering through extreme heat and disruption to a major intersection.

The North Terrace and King William intersection upgrades are expected to be completed on schedule by January 15, Transport Minister Stephen Mulligan says.

The work has caused significant disruption for commuters, closing down one of Adelaide’s busiest intersections for two weeks.

‘This is a major undertaking, we are working 24 hours a day, seven days a week over a two-week period to get into the intersection, get the work done and then get out,’ Mr Mulligan said.

In a move criticised by the opposition the government previously ruled out a right turn from King William Street into North Terrace saying it would add another $20 million to $30 million to the project.

But opposition transport spokesman David Pisoni said the project was being rushed to be ready before the March state election.

The project will deliver a one-kilometre extension along North Terrace, from King William Street to East Terrace and an extension along King William Road to the Adelaide Festival Plaza precinct.

The government will also purchase three additional trams.