At the moment, the ACT plans to run the trams wire free only as far as Sydney Avenue in Barton, using wires from there to Adelaide Avenue.

But Mr Guida, who appeared before a federal parliamentary inquiry on Thursday evening, said nothing should impede the view of Parliament House.

“One of the major views of the flag mast is from Canberra Avenue coming from the Manuka area, and if we don’t have wire free until we get to Adelaide Avenue you’ll see the mast through the drooping wires,” he said.

Transport Canberra director general Emma Thomas said the government was speaking with manufacturers about how far trams would be able to travel without wires as technology improved.

“Any distance or hills puts at risk the vehicle’s ability to store enough energy to get to the next stop. And that’s our main concern is to make sure that technically we’re able to make the distance. And it can't just make it, because if there’s any hold ups with traffic or another things we might be in a circumstance where people can't move when they're on a light rail vehicle," she told the inquiry.

Mr Guida, of architects Guida Moseley Brown, is the "moral rights holder" in the design of Parliament House and the surrounding landscape, but said he had not been formally consulted by the ACT government. His only contact had been an “informal briefing” offered after he raised concerns about the design to the federal inquiry, and very preliminary consultation three years ago.

He revealed that the ACT government had raised the idea then of having the tram running straight up Commonwealth Avenue, with a stop in the “cutting” of State Circle, and a lift to carry people up to Federation Mall between old and new parliament house.

The station could have been underground, with talk of building a “parallel tunnel” to the State Circle tunnel, with the lift appearing on Federation Mall on the side of the road, in the area taken up with small parking spots. He had no objection to that route, which made sense for commuters, he said.

He called on the government to reconsider its stop at King George Terrace, which was more than 800 metres from Parliament House and would “discourage a great many users”, he said.

“After 400 metres people’s usage of public transportation really starts to drop off,” he said. “I know that rail enthusiasts will say that people walk further for rail but the examples around the world show that after 400 metres it drops off fairly quickly."

The planned Barton stop did not create a clear pathway for pedestrians, he said, suggesting the tram could run around State Circle rather than crossing into Capital Circle. That would allow a stop at Melbourne Avenue, just 300 metres to walk to Parliament House.

The National Capital Authority told the inquiry it would need to employ extra staff and a bigger budget to assess the project – and it expected the ACT government to pay its costs.

Authority chief executive Sally Barnes said the ACT had not provided its definition design until February, when the plan was to take over a traffic lane on Commonwealth Avenue for the tram. The authority was concerned about the impact on the wider city road network as well as the ceremonial routes and the ACT had now changed its model to build a new, separate Commonwealth Avenue bridge and use the median strip.

The authority had only seen a "schematic" of the new plan, with no detailed drawings or engineering or traffic work.

"So we haven’t at the moment got anything to assess,” Ms Barnes said. “Rather than just have the schematic we really want to be quite certain about things like furniture … the details around lighting. We’ll need a lot more of that detail about the project before we can assess it.

Chief planner Andrew Smith said the ACT’s latest images were very different to the technical material provided earlier.

“So at this stage we are not clear on what the proposal really is,” he said.

Despite the authority's reservations about Commonwealth Avenue, the ACT government has discounted the Kings Avenue route.

“The ACT government has indicated that it would be unlikely to invest in the project if it’s forced to go down Kings Avenue," ACT Transport deputy director Duncan Edghill told the hearing. "So there might not be a whole lot of benefit in spending time and resources on examining different route options. It would make more sense to us if it was, “is this particular route going to be acceptable or not?””

Mr Edghill said the ACT was open to "tweaks,” including switching from Capital Circle to State Circle “but wholesale changes would become less attractive to the ACT government”.

Inquiry chairman Ben Morton (Liberal) said it made no sense for the ACT to produce a large amount of detailed work on the Commonwealth Avenue route before the National Capital Authority had even agreed to the option.

Ms Thomas said detailed design work would be done by the private sector consortium after the tender.

Asked about the plan discussed with Mr Guida to head up Commonwealth Avenue to State Circle, the ACT authorities said the option ran into trouble with the heritage stone wall at the cutting, and with traffic and intersections on State Circle, as well as access to the national institutions closer to the lake.

Inquiry member Julian Leeser (Liberal) asked why the ACT hadn’t considered underground rail, to which Ms Thomas said the project was not only a transport solution but an “urban-renewal land-use solution”.

Mr Edghill said light rail could “enhance the urban realm”, to which Mr Leeser said “beauty is in the eye of the beholder” and the goverrnment's picture of a tram in front of old Parliament House was “provocative”.

He questioned the “vandalism” of putting light rail on the important vista leading to the parliament’s “front door” rather than the “back door” of Kings Avenue.