The long awaited pedestrian and cyclist underpass at Bowen Place near Lake Burley Griffin has been officially opened.

From Friday, walkers, joggers and cyclists will be able to do a bridge to bridge lap of the lake without crossing any major roads.

The $10 million underpass which began construction in 2013 was completed 6 months later than expected but came in under budget.

Chief Executive of the National Capital Authority, Malcolm Snow said the new path addresses serious safety concerns for pedestrians.

Chief Executive of the National Capital Authority, Malcolm Snow, said the new path addresses serious safety concerns for pedestrians. ( ABC News: Mark Moore )

"Safety was the primary driver for this (underpass)," he said.

"The cars now have their own separate system and cyclists, pedestrians and walkers are now in a very safe environment and can enjoy the wonderful setting."

The underpass includes a 300 metre path connecting Kings Avenue to the existing path network next to Lake Burley Griffin, allowing pedestrians and cyclists to pass underneath the existing road.

ACT Senator Zed Seselja said the underpass was a welcome improvement.

"Getting across that road can be quite dangerous, so now that's fixed, people will really have wonderful amenity as they get around the lake," he said.

"Its a very popular walk, its a very popular run or ride and this will make it far easier."

The underpass also includes clear markings to encourage separation of cyclists and pedestrians.

The underpass was originally planned for completion in time for the centenary celebrations, but the project was pushed back to help fund other repairs in the capital at that time.