Canberra's Commonwealth Avenue bridge should be replaced with a new model in order to accommodate the city's growing population, a leading engineer has said.
Greg Taylor, the chair of the civil structural committee at Engineers Australia, has welcomed news the famous bridge could be rebuilt in order for the Canberra light rail to cross Lake Burley Griffin.
"A new bridge is a positive outlook and a good decision," Mr Taylor said.
"From an engineering perspective, you would be able to use better materials and extend the life of the bridge and reduce maintenance costs by building a new one."
The reaction comes as the National Capital Authority revealed it would look at building of a new bridge over the lake to accommodate stage two of the light rail to Woden.
The territory government had been planning on building a bridge in the centre of the existing Commonwealth Bridge to accommodate light rail, after the NCA said they would not be able to use any of the road lanes.
Transport Minister Meegan Fitzharris said the authority 's announcement had taken her by surprise.
She said the territory government would continue putting together the business case for the second stage of light rail based on building a bridge in the middle of the existing structure, but the authority should consider all options.
"From our point of view there are some really critical aspects of that bridge whether or not we're building light rail and that's the heritage value of that bridge, the very important part the bridge plays in the parliamentary triangle," she said.
"I think for the community of Canberra that bridge is a much loved bridge that the community would want to know and need a pretty good case for the replacement of."
A spokeswoman for the National Capital Authority said it was too early to say whether a building a new bridge would be less disruptive or expensive that modifying the existing one.
But Mr Taylor said a new bridge would also allow for safer travel for pedestrians and cyclists.
"If you look at the bridge at the moment, it's a good bridge but it has constraints to a point where it's unsafe," he said.
"People walking over the bridge can be hit by a cyclist, and some aspects of the bridge are a bit outdated."
Ankur Sharma, an engineering lecturer at the Australian National University, said readjusting the current bridge to allow for light rail tracks would be a safety risk.
"If a metro line ran over the current bridge, it would cut the lifespan of it by 20 to 30 per cent easily," Mr Sharma said.
"It wasn't designed to withstand such heavy loads and strength of the bridge would be degraded."
Mr Sharma said bridges like the Commonwealth Avenue bridge had a lifespan of around 100 years.
UNSW Canberra civil engineering lecturer Dr Safat Al-Deen said building a new bridge would require the existing one to be closed to traffic for a year minimum, as it would need to be put in the place of the existing one so it did not "mess up" the alignment of the Parliamentary Triangle.
While that would cause "significant traffic disruption", Dr Al-Deen said a temporary bridge could be built for traffic to use.
"Temporary bridges are used all the time in defence and military," he said. "It's not a big distance, it's only 325 metres."
Lake Burley Griffin Guardians member Juliet Ramsay said the current bridge should remain in place, with a tunnel built underneath the lake as an alternative.
She said replacing the bridge with a new one to accommodate the light rail would damage Canberra's heritage.
"It almost seems a brutal thing to do. It's a fabulous bridge in its own right and there's an elegance to it," Ms Ramsay said.
"There are lots of concerns. There is a lot of significance with the bridge and it should be heritage listed."
Mr Taylor said a redesigned Commonwealth Avenue bridge would have the potential to showcase Canberra to the rest of the country.
"Other considerations for the bridge should be taken into account, such as places to place fireworks for displays or lighting," he said.
"The bridge could have an outstanding facade which can signify Canberra in advertising."
Commonwealth Avenue Bridge opened in 1963, the fourth to be built in that location but the first to cross the new Lake Burley Griffin.
The previous three crossed the Molonglo River, before it was dammed to create the lake.
Then-Prime Minister Robert Menzies described the bridge as the "finest building in the capital" at its official opening.
The bridge also contains four granite stones from the original Waterloo Bridge in London that was built in 1817 before it was demolished to make way for a new one in the 1940s.