Strict National Capital Authority planning rules mean the proposed extension of Canberra's light rail to the Defence precinct at Russell would run without the use of overhead power lines.
The ACT government has given strong indications it wants to extend stage one over the 3.2 kilometre route to Russell, adding three passenger stops and creating about 5600 extra passenger trips each day – a boost of 30 per cent to the network.
While the Northbourne Avenue route to Gungahlin will have overhead wires, Canberra's trams are likely to be adaptive to power from underground rails, large rechargeable batteries or super capacitor technology.
Capital Metro Agency executive director for procurement and delivery Stephen Allday said the federal authority's requirements meant trams running from the planned city terminus at Alinga Street would need to be wire-free from around London Circuit, down the upgraded Constitution Avenue and up to Russell.
The more expensive technology will be included in additional bid information due with the government at the end of the month. The two consortiums shortlisted by the government delivered bids for the first 12 kilometres last week.
"Obviously the Russell element involves a lot more NCA-controlled land and Constitution Avenue, particularly with Anzac Parade there, is extremely important to them.
"That's why they said it would have to be wire-free, so we took that on board," he said. "We can make it work, and it will work, but the sensible place to do any transition from wire to wire-free is the Alinga Street terminus."
Any future route across Lake Burley Griffin is also expected to run without overhead wires.
The consortiums are free to choose their preferred technology for wire-free tram lines. Two methods run from ground technology, a "third rail" supply or induction power, or on-board batteries charging at stops.
Mr Allday said ground power was considered the most expensive option.
The project's business case, released a year ago next week, does not require overhead wired or wireless power systems for the main route but notes cost and technological risk mean overhead 750 volt direct current power supply is likely to be used. The power lines should be "potentially discrete".
"We've worked with the National Capital Authority very closely all the way through, and that's important because we need them to come along the journey with us," he said.
The government believes trams could service about 8300 public servants and Defence Force personnel based at Russell, as well as city office workers, tourists and shoppers. The extension would also service new housing developments in Reid, the convention centre and Canberra Institute of Technology.
Any extension will see the $783 million project cost and annual consortium payments grow, but could improve value for money.
Damien Haas, chairman of the ACT Light Rail group, welcomed examination of the extension plan.
"Using wire-free light rail to travel across areas of national significance like Anzac Parade and the bridges across the lake is understandable from an National Capital Authority perspective, although I think modern catenary wire systems are already unobtrusive," he said.
"This technology is already in use in other cities, and is an area of intensive research.
"Although light rail using batteries or super capacitor can only travel 20 to 25 kilometres before recharging, other systems like the one in Tours, France using a third rail in the road surface deliver the same wire-free visual aspect, without an impact on vehicle range."
Mr Haas said Canberra would be the first Australian city to use the technology, potentially creating a new local industry.