Vehicles with at least two people have been using the transit lane to pass heavy traffic during the completion of the Gungahlin Drive Extension.

Roads ACT director Tony Gill said with the GDE now fully open to traffic, the T2 transit lane on Adelaide Avenue between Melrose Drive and State Circle would return to being a bus lane.

''The T2 transit lane was introduced in 2009 as a temporary measure to help alleviate increased congestion on Adelaide Avenue associated with construction work on the GDE by encouraging people to car pool or travel together,'' Mr Gill said.

''The completion of the GDE means there has been a reduction in traffic congestion arterial roads such as Adelaide Avenue. As such, the bus lane will be reintroduced.''