Releasing the route options, on which he wants feedback, Chief Minister Barr confirmed the ACT was asking for federal funding for the project as part of "city deal" negotiations. But he would not say whether the project depended on federal money to go ahead.

This flyover was produced by Fairfax Media and is indicative only.

National Capital Authority chief executive Malcolm Snow pointed to the possibility of a third bridge to carry the light rail tracks in the void between the two structures that make up Commonwealth Avenue bridge. He said while he hadn't seen the detail for Commonwealth Avenue bridge, one option used the two existing bridge structures and another built an entirely separate bridge in the void between them. The void was wide enough, but each option had design challenges.

Mr Barr urged the federal government to come to a quick decision on a city deal, and said the ACT had a "better than normal chance of a securing a good outcome" given the Commonwealth would also make money from land sales.

"They have a sharp eye clearly to the financial to the return to their own budget, so this is where is see a significant opportunity for them in a Canberra city deal," he said. "Because they own a lot of land. They have already indicated that they want to dispose of some of that land. They're selling it. They could increase the value of that land through a partnership city deal with the ACT government for transport infrastructure."

The main question for debate in the routes released on Monday is whether to go straight around Capital Circle from Commonwealth Avenue, or take a detour through Barton. The longer route would travel past Old Parliament House and cross Kings Avenue to National Circuit. It would loop along National Circuit past the Kurrajong Hotel, the Realm hotel and government office blocks to Canberra Avenue before joining Capital Circle and on to Adelaide Avenue.

The government is considering two endpoints - the Woden town centre or heading on to Canberra Hospital along Hindmarsh Drive.

Mr Snow said the project fed into the authority's own thinking about the future of Commonwealth Avenue, which "could be a different type of road environment of which light rail could be an integral part", he said.

But he made it clear that no trees could be removed from in the median strip in front of the Hyatt Hotel leading up to Parliament House. The cedars were very old and significant plantings.

"We're not not removing trees, it's not a Northbourne Avenue scenario," he said. "The trees in Commonwealth Avenue on southern side are extremely significant trees. They're very old trees and will need to be retained."

Mr Snow also confirmed the trams must be wire-free from the time they left the Northbourne Avenue terminus, until a point yet to be determined down Adelaide Avenue.

We have said quite clearly and said quite some time ago to the ACT government ... there would be no overhead catenaries," he said. "...Would we really want wires around the entrance to the Lodge? Probably not."

The National Capital Authority supported light rail, which was "another addition to the transport modes that a modern innovative city should expect", and was open to either route.

"If one of the functions of light rail is to move through concentrated areas of high employment then you would think that a route that had an option of going through somewhere like Parkes and Barton would be attractive in terms of picking up passengers, but it's a balancing act ... because a route through Parkes and Barton would no doubt add travel time."

Transport Minister Meegan Fitzharris said the government would consider the stage 2 routes in terms of their patronage, cost, proximity to employment, entertainment and tourism spots, and options for urban renewal.

The government has not released its early costings. Ms Fitzharris said the cost was comparable to stage 1, for which construction is $707 million. But stage 2 was the most complicated route of the network because of the lake crossing and the parliamentary zone.

"We've said it's going to be comparable, but there are come challenges," she said.

Preliminary engineering work gave the government a high level of confidence about the ability to cross the bridge - using the southbound lane for the southbound tram and the northbound lane for the northbound tram.

"It is certainly not a barrier at all to light rail," she said of the lake. "In fact, we know we can get across the lake with light rail without needing to build a brand new bridge."

The government's preferred route travels west around London Circuit, and Ms Fitzharris said the idea was to link into the western side of the city because any future stage would travel through the eastern side.

Mr Barr said the next leg after Woden would be an east-west crossing - from the city to the Russell area, possibly from Belconnen.

The route is expected to be finalised this year, with contracts signed before the 2020 election.

Flyover produced by Scott Hannaford