The long-awaited light-rail link between Civic and Woden has hit a new roadblock after a senior federal official conceded that heritage values may block the existing proposals.

Six years after Canberrans were first consulted about possible routes, planners still lack an option that satisfies both the ACT government and the National Capital Authority (NCA), which controls the parliamentary area that light rail must travel through.

ACT Transport Minister Chris Steel said today he would continue to work with the NCA on a viable route, but could not yet say where that might be.

"We'll be consulting with the community, we expect next year, ahead of the environmental impact statement being delivered," he said.

NCA chief executive Sally Barnes told federal parliament yesterday that new technical difficulties had emerged in linking light rail from Commonwealth Avenue to State Circle, a road near Parliament House lined by heritage-listed rock cuttings.

Ms Barnes said the engineering challenges might be too difficult or too expensive to overcome, and the NCA was now open to looking elsewhere.

State Circle was the Commonwealth's preferred route, because it would be faster and was thought to have minimal impact on the area's heritage and aesthetic values.

The NCA initially argued against an alternative route — which had been favoured by the public — which went past Old Parliament House (OPH) and through Barton, where many Canberrans work.

The NCA said that route was more visually disruptive to OPH and the surrounding area.

The authority also cited aesthetic values when it ruled out the use of overhead electrical wires in the parliamentary zone.

Canberra's existing light-rail vehicles rely on this wiring for power, though the ACT government has arranged to buy new vehicles with batteries for the short journey near parliament.

On ABC Radio Canberra today, Ms Barnes was asked whether heritage and aesthetic values could stop a Woden light-rail link from being built at all.

"I don't know," she said.

"If the heritage experts who look at it through the [federal Environment Protection and Biodiversity Conservation Act] lens say 'you're not able to manage the heritage impacts adequately', all of us will have to go back to scratch and say … 'is there another way'."

Barton route divides light-rail supporters

Canberra's light-rail network has been a contentious issue in the past three ACT elections.

The Liberals remain opposed to extending the network south to Woden, saying it is too costly at present.

They also highlight the government's refusal to release a business case and benefit-cost analysis for the Woden route.

However, both the Commonwealth and ACT governments have funded the network, saying it is crucial for Canberra's future.

Ms Barnes said light rail was compatible with the Griffin plan — Canberra's founding design document — and the NCA wanted efficient public transport into and through the parliamentary area.

"But we would like to maintain the heritage values as much as possible," she said.

"It has to be a [shared] system."

She also said light rail in the parliamentary area would need to be significantly slower than north of the lake, as the vehicles would travel through shared pedestrian zones.

Mr Steel said technical challenges were to be expected in large projects like the light-rail extension and the government would find a way to proceed.

Neither the ACT government nor the NCA would nominate a preferred route when pressed.

However, Mr Steel noted the community-preferred line through Barton remained workable.

"We think it would be cheaper to deliver and provide closer access to public transport for the tens of thousands of employees who work in the parliamentary triangle."

Meanwhile, the Public Transport Association of Canberra said dropping the State Circle option would be disappointing.

Its chair, Ryan Hemsley, said Woden commuters wanted as fast a journey as possible.

"The needs of public transport users shouldn't be sacrificed for the sake of project-delivery convenience."