Shared paths along Commonwealth Avenue bridge will be widened and the overall structure strengthened under a National Capital Authority plan to extend the life of the 60-year-old structure to cope with heavier vehicles and more traffic.
The authority has released early plans for the $137 million project, saying it wants community feedback before it makes a formal submission to the Federal Parliament's standing committee on public works.
The project includes widening the two spans of the 310-metre bridge outwards, leaving the internal gap free for a new bridge to handle light rail.
The plans also include changes to pedestrian approaches to the bridges and the loss of a car park on the north-eastern side.
The bridge will retain three lanes for vehicles in each direction.
The authority expects work to begin on the project in 2024 and for it to be completed sometime in 2025, depending on the approval process.
National Capital Authority chief executive Sally Barnes said the bridge, which had been designed in the 1950s, was an engineering masterpiece but forecasts for increased traffic meant it needed to be strengthened.
The authority is yet to settle on how traffic and bridge closures will be managed through the project, saying these plans will be finalised once a contractor is selected through an open tender process.
Project director Greg Tallentire said when the bridge was designed, cars weighed 800 kilograms on average, but modern special utility vehicles and electric cars could weigh around 3000 kilograms.
The works would increase the strength around the pylons by 54 per cent and the stretches between pylons by 12 per cent, Mr Tallentire said.
The internal structure of the bridge would also be strengthened with additional concrete. Mr Tallentire said the additions to the bridge would complement the existing architecture.
Ms Barnes said the decision to have a wider shared path reflected the concerns of cycling advocates, who had opposed having an on-road cycle path.
Pedal Power executive director Simon Copland endorsed the plans and said they would help increase active travel over and around the bridge.
"We welcome the plan to increase the width of the shared path on Commonwealth Avenue Bridge to five metres," Mr Copland said.
"Commonwealth Avenue Bridge is an extremely busy cycling and pedestrian link, with people both using it to take a leisurely stroll or ride around the lake or for their daily commute.
"The current bridge footpath is too narrow, slowing cyclists down and creating often dangerous interactions between pedestrians and cyclists. The increased width of the shared path to five meters will significantly alleviate this problem. We also ask the NCA to ensure there is clear markers separating cyclists from pedestrians on this shared path."
The federal government in January 2021 announced $137 million in funding for upgrades to Commonwealth Avenue bridge.
Infrastructure Australia added the bridge to its list of priority projects for Australia late in 2020, saying the project had a "strong strategic and economic case" and would deliver a "net benefit to the economy".
Engineering and development consulting firm SMEC was awarded the contract to design the works in October 2022.
The National Capital Authority will hold consultation sessions on Thursday, Friday, Saturday and Sunday near the bridge.
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