Adelaide has earned a reputation over the years for some questionable decision making when it comes to urban planning.

It is, after all, the home of Australia's one-way highway (the Southern Expressway's lanes have since been duplicated, but the humiliation lingers).

The latest project to raise the ire of locals involves a decision to shut one of the CBD's biggest thoroughfares to traffic during the summer holiday season.

From 10:00pm on New Year's Day until 6:00am on January 15, the North Terrace-King William Street intersection will be out of action for cars and buses.

Tram users will have to wait even longer — substitute buses will run along an alternate route between the Entertainment Centre and Victoria Square until January 22.

The closure is to allow for works on a tramline extension that, once finished, will still require passengers to transfer from one tram to another to take them along a route that is already covered by dozens of buses.

Loading...

Adelaide Lord Mayor Martin Haese described the timing of the project as "good", before adding a more qualified appraisal.

"It's probably the best time over the course of the 52-week year to do those tram works, noting that it's never a great time," he said.

Loading

Once completed, the extension will take the tramline another 350 metres north to the Adelaide Festival Plaza and 1 kilometre east to East Terrace.

But northbound tram passengers wishing to get to the East End will have to disembark before boarding another eastbound tram, because of the Government's decision not to install a right-hand turn at the King William Street intersection.

That's despite the fact that old footage clearly shows trams turning right before the track was ripped up.

More than 40 bus routes will be affected and detours mean commuters will have to walk hundreds of metres to stops in other streets.

Sorry, this video has expired Why was Adelaide's extensive tram network ripped up in the 1950s?

Transport Department spokesman Paul Kermode defended the works, but did not divulge how many complaints the department had so far received.

"We believe starting at this time gives us the best window to get the work done," he said.

"This is a time when traffic on the roads is traditionally a bit quieter, it's during school holidays and uni holidays.

"We've got some events coming up including the Tour Down Under, which has a stage that goes through the city on January 17."

Mr Kermode added that it would have been far worse to carry out the works in the Mad March festival season.

But while authorities hope to extend the network further into the inner suburbs, residents along the Gawler rail line have been waiting for more than five years for long-promised electrification.