Mount Barker's Heysen Boulevard is supposed to be a vital transport corridor, but the 9-kilometre ring-road in the Adelaide Hills town looks more like a dotted line.

"It's a boulevard that goes nowhere," Mount Barker Mayor Ann Ferguson said.

"We have these gaps where you can't get across. It stops and starts — it's a nightmare."

The reason for the boulevard's patchiness dates back to 2011, when the former Labor government decided to rezone agricultural land to allow urban growth.

The controversial decision put developers in charge of building sections of road on the land they purchased.

Including six major developers, there are more than 90 landowners across the 1,300-hectare site.

Ms Ferguson said coordinating construction of one connected road with all the owners was "almost impossible" for the council to do, partly because it had not yet acquired the land, or because the developers were not yet ready to build.

A decade on, it is a boulevard of broken roads.

"It's a real issue for our community to get across Mount Barker because people who want to get onto the [South Eastern] Freeway have to rat run right through the town, causing congestion," Ms Ferguson said.

She said the congestion would only worsen as Mount Barker's population grew. The town is expected to hit 60,000 by 2036.

The growth is being spurred by urban development, with the council processing about 1,000 development applications per year.

Calls for state government to intervene

Liberal turned independent MP Dan Cregan accused state governments of both persuasions of not investing in Mount Barker's growing needs.

"I became an independent because I felt there wasn't sufficient investment in my community," he said.

Both the Mayor and Mr Cregan have called on the state government to seize control of Heysen Boulevard from developers.

"This is a vital connector road, and without sufficient investment to see this project through, we're going to see local and acute congestion," Mr Cregan said.

"The Minister for Infrastructure and Transport (Tom Koutsantonis) has the power to take care and control of the project and make it a state road.

"There are other steps he can take, including injecting state funds and seeking a Commonwealth contribution."

Ms Ferguson said it would cost more than $100 million to link the remaining 4 kilometres of boulevard, a cost that was too great to pass onto ratepayers.

"I am hopeful that this government will hold our hands and we'll move forward," she said.

"I would like them to bankroll [the project] and as the money comes back from the separate rate, we can pay the state government back."

The state government has been contacted for comment.