The National Capital Authority announced the temporary measure, set to be finished within two weeks, due to growing concern about pedestrian and cycling safety on the western side of the bridge.

While the central basin loop side has a higher safety railing implemented "many years ago" due to increased usage, path users on the west basin side have only a half-metre barrier between them and often-heavy traffic.

The low railing has been an issue for about five years, since an accident resulted in a cyclist being thrown from the path and into oncoming traffic on the bridge.

Pedal Power spokeswoman Rachel Lynskey said the issue had been raised by a member of the group as recently as March, after a gust of wind threw the cyclist off course.

"When it's windy you can easily get blown in the wrong direction," she said.

"It's not a smooth surface along the bridge, You can feel quite at risk of falling into traffic."

Ms Lynskey said Pedal Power was very happy with the decision to implement the safety barrier, which would be about 1.4m, more than double the height of the existing barrier. The two-rail system, with handrail and cycling restraint, would be bolted to the path next to the existing rail.

The new measure would be installed temporarily at a cost of about $160,000, and would be painted grey to meet heritage requirements.

Pedal Power was one of a number of cycling bodies consulted about the plans.

Ms Lynskey said she was looking forward to a permanent solution being adopted, in line with improvements to the area as a whole to make the Parliamentary Triangle more pedestrian and cycling friendly.

National Capital Authority chief executive Malcolm Snow said the authority had been looking at ways to improve public safety on the bridge since the accident in 2012.

At the time, preventative action was taken to reduce the speed limit for cyclists and erect signage to proceed with caution. Due to increased usage, the barrier is being put in place.

"We're aware on the west basin side the ACT government is working constructing a new park, playground, improved facilities on the northern side of Commonwealth Bridge so we would expect that there would be an increase in the volume of both cyclists and pedestrians using the western footpath on the bridge," Mr Snow said.

He said the new railing was of significantly lower cost than others considered and it was easily integrated into the bridge structure.

Mr Snow said the decision to make the railing temporary was due to the open consultation about the NCA's plans to improve conditions on both the Commonwealth Avenue and Kings Avenue bridges.

He said the light rail alignment decision was "completely unrelated".

"It is expected the temporary safety barrier will be in place for around two years, until the longer-term design and road management plan, outlined in the Kings and Commonwealth avenues draft design strategy, is finalised after public consultation," Mr Snow said.

There will be minimal impact on motorists, with the majority of work to be undertaken at night during the next two weeks, beginning on Monday. One northbound vehicle lane and half the shared pathway would be closed during the night works.