Brisbane's Airport link tunnel will take fewer vehicles than expected from Kingsford Smith Drive, Brisbane councillors were told this morning.

The tunnel, linking the Inner City Bypass to Brisbane Airport, will only divert about five per cent of the 70,000 vehicles expected on Kingsford Smith Drive by 2026.

The news ups the political ante over the city's key riverside connection to the airport.

Previously Brisbane City Council traffic projections predicted Airport Link would draw between 15 and 20 per cent of traffic away from Kingsford Smith Drive.

But Transport Infrastructure manager Alan Evans this morning reported that recent modelling had substantially changed the traffic situation.

"It was expected to be around 20 per cent," Mr Evans told the meeting.

"Now it's down to five per cent," he said.

The news comes as some Brisbane councillors got their first look at the most recent modelling of "double decker " tunnels, fixed "pedestrian and cycling viaducts" in the river, attempts to widen Kingsford Smith Drive to six lanes and 25-metre "expressway" extensions into the river which could provide an extra three lanes.

Deputy Mayor Cr Graham Quirk said 25 different designs had now been considered by planners.

This morning Cr Quirk revealed poor soil under the strip of Kingsford Smith Drive near the Breakfast Creek Hotel would prevent a tunnel being built under the roadway.

Cr Quirk said one proposal for the double-decker tunnels was for them to be built off-site and then effectively buried beneath the river edge, but not under Kingsford Smith Drive itself.

Mr Evans said this option also allowed the 60,000 vehicles to continue to use Kingsford Smith Drive.

Under this proposal, the road level traffic set-up would remain, but two levels of two-lane tunnel would be built underground beside Kingsford Smith Drive and not directly under the road.

Cr Quirk said it was still too early to say if the off-river tunnel option was the best solution for Kingsford Smith Drive, when pressed by Labor's Council Opposition Leader, Cr Shayne Sutton.

"This is going to be a very long journey," Cr Quirk said.

Other options include:

- a six-lane widening of Kingsford Smith Drive, which has problems with river silt;

- a separate three lane widening or "viaduct" on piles over the river; or

- a fixed pedestrian and cycling "viaduct", which is not floating, but would not provide extra lanes.

brisbanetimes.com.au revealed in February that Lord Mayor Campbell Newman was looking again at a tunnel under Kingsford Smith Drive because of the traffic growth from the nearby Hamilton Northshore development and the airport.

Brisbane City Council has set aside $21 million for introducing six-lane sections of the Kingsford Smith Drive closer to the Gateway Motorway and 30 per cent through the project.

It has lodged a submission for more than $600 million to the Federal Government for funds to revitalise Kingsford Smith Drive.