The National Capital Authority has assured residents near the new ASIO headquarters that local roads will be able to cope with extra traffic when staff move into the building early next year.

But some Campbell residents fear that Constitution Avenue will be turned into ''another Gungahlin Drive'' after the ASIO building is occupied and other sites along the street are developed.

Most staff at the new ASIO building who drive to work will enter the Russell Defence complex through the existing main entrance at the end of Kings Avenue or by turning from Parkes Way on to Anzac Parade and then on to Constitution Avenue.

Mark Anderson, who represents several dozen Campbell residents, said locals had been told the ASIO building would have about 1100 parking spaces.

While many of the staff already worked in the existing ASIO headquarters at Russell, others would be moving to the new building from other sites.

Mr Anderson said Constitution Avenue would not be able to cope with increased traffic.

''We just see Constitution Avenue becoming quite a muddle,'' he said.

Mr Anderson was also concerned about the impact of planned developments for Constitution Drive, including the proposed redevelopment of RSL headquarters and the construction of apartments on a 6.4 hectare greenfields site.

''There's an awful lot of traffic coming into the area and the road isn't being fixed in advance to cope with it,'' he said. ''So we just see it as being another Gungahlin Drive, where people are going to be brought to the area but the infrastructure is not going to be able to cope. Then there will be a hue and cry and then finally someone might do something about it.''

NCA chief planner Andrew Smith said works to improve traffic flow on the Anzac Parade end of Constitution Avenue would be completed well in advance of the ASIO building being progressively occupied from February or March next year.

The improvements included widening the road to three lanes at turning points.

Cars turning right at traffic lights from Anzac Parade to Constitution Avenue would no longer be stopped by a second set of traffic lights after they turned. Mr Smith said the increased traffic would be ''managed to acceptable standards''.

''We know the issues that are going to arise and we're dealing with them now,'' he said.

Mr Smith said the road system could manage the traffic generated by significant amounts of development in Russell or Barton.

''We can comfortably cope with another 500,000 square metres of offices being developed in either Russell or Barton,'' he said.

A report by SMEC Australia for the NCA found that road network changes, including the completion of the ASIO building, would generate a modest increase in traffic entering and exiting Campbell.