A parliamentary committee has recommended a $137.5 million upgrade to Commonwealth Avenue Bridge be approved, but expressed concerns the National Capital Authority's plan won't keep pace with growth in Canberra.
The NCA, which oversees planning in the parliamentary triangle, will strengthen and widen the bridge connecting Parliament House to Canberra's city.
Works will include increasing the load-bearing capacity of the bridge, upgrading vehicle and safety barriers and widening the pedestrian and cycle pathways, in a project planned to future proof the infrastructure for at least 50 years.
While the Public Works Committee recommended the works go ahead, it did raise concerns "that the level of strengthening may not sufficiently future-proof the bridge".
In a report presented to the House of Representatives on Tuesday, the committee questioned the NCA's decision not to demolish the bridge and build a new one, which could facilitate the ACT government's planned light rail extension.
Known as Light Rail stage 2A, the extension will involve the eventual construction of a new inset bridge over Parkes Way in between the two Commonwealth Avenue bridges.
But work on the extension is unlikely to begin before 2030, and the NCA said engineering advice "suggested that the strengthening work needed to be undertaken within a shorter timeframe to avoid reaching failure of the existing bridge".
Works will also mean the bridge can be used by heavy vehicles up to 42.5 tonnes, allowing an estimated 8000 trips per hour across the bridge by 2036.
However, the committee noted the bridge would not be strengthened to an industry standard allowing even heavier vehicles of up to 160 tonnes.
"Firstly, the Committee notes that the Commonwealth Avenue Bridge will be strengthened to the 1992 Austroads Bridge Design Code and not an SM1600 load that can carry heavier vehicles," the committee's chair, Labor MP Graham Perrett, wrote in the report.
"Secondly, the Committee notes the NCA's decision to strengthen the existing bridge rather than demolish and replace it with a much more costly new structure that contains the proposed light rail system.
"The Committee acknowledges the level of uncertainty around extensions to the light rail, however remains concerned that the three-bridge proposal may prove impractical or impossible given the complexity of the design.
"For these reasons, it may be that the bridge will still require demolition and replacement in the future, rendering this expenditure redundant."
The committee recommended the NCA report back with written updates every six months until the project was completed.
It also recommended the authority contact local federal MPs to offer project briefings and updates, after Bean MP David Smith scolded officials for failing to do so at a public hearing in August.
The report ultimately recommended the House of Representatives approve the project, with the committee "satisfied that the project has merit in terms of need, scope, and cost".
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