THE operators of Brisbane Airportlink have gone under with debts of more than $3 billion but the toll road will continue to operate as normal.

The board of BrisConnections called in voluntary administrators this morning, shortly before bank investors in the project appointed PPB Advisory as the receiver managers of the project.

It follows a trading halt last November when BrisConnections' CEO Ray Wilson revealed the company's debts were greater than the value of the asset.

Today, a statement given to the Australian Securities Exchange said BrisConnections had submitted "detailed restructuring proposals to the group's lenders but the majority of lenders were not prepared to support the proposals".

"It is disappointing that the Board has had to reach this decision," said BrisConnections non-executive Chairman Trevor Rowe.

"The Airportlink M7 is unquestionably a world class piece of transport infrastructure that will continue to support Brisbane's growth into the decades ahead."

Overblown traffic forecasts have been blamed for the project's financial failure.

Traffic forecaster ARUP projected that 135,000 vehicles a day would use the Airportlink a month after opening, growing to 190,000 within six months of operation.

In December, an average of 47,102 vehicles a day used the tunnels, which currently carry discounted tolls of $2 and $2.50.

Paul Turner from motoring group RACQ said the forecasts were "far too ambitious".

"It was unrealistic to expect Airportlink would attract higher traffic volumes than the Gateway Motorway (which carries about 100,000 vehicles a day)," Mr Turner said.

But he said there would be no initial impact for motorists.

"The tunnel has proven its worth in reducing congestion around Brisbane roads since its opening and the announcement that it will continue to operate as normal is good news for motorists," he said.

At last count, about 45,000 vehicles a day were using the $4.8 billion roadway, 90,000 fewer than forecast.

Traffic volumes have declined steadily since the end of the toll-free period, despite the introduction of a discounted toll.

The tolls of $2, and $2.50 are due to increase in mid-April before rising again in October.

Operators had hoped the staggered introduction of the full-toll would help boost traffic volumes.

It is the second tollway to go broke shortly after opening.

In February 2011, receivers were appointed to RiverCity Motorway, who operate the Clem7 Tunnel.

A buyer has still not been found for the tollway which carries about 25,000 vehicles a day.