Chair of the ACT Light Rail advocacy group, Mr Haas said the government should commission plans for an extension as soon as it signs a contract for the planned 12 kilometre line linking the city and Gungahlin.

The possible extension is being considered by Capital Metro Agency officials now.

Adding approximately 4.5 kilometres would allow extra value to be achieved from the cost of planning and constructing the first stage line, building depots and other infrastructure and the purchase of rolling stock.

"It also helps resolve a lot of policy options right now, which include paid parking in the Parliamentary Triangle and the complaint that Gungahlin to the city light rail only delivers workers into Civic.

"Certainly if people are transiting by bus, being able to use light rail would provide advantage to everybody," he said.

Releasing the business case for the $800 million line last month, Capital Metro Minister Simon Corbell said a separate business case would be prepared for a possible Russell extension.

Mr Haas backed the plan and said further extensions to Parliament House and Canberra Airport could eventually run from the lines to Russell.

The ACT Light Rail group has monitored government policy on transport for years and Mr Haas facilitates an active membership and social media presence. He has met with Capital Metro officials and members of various territory governments and oppositions.

"There are a lot of Defence families who live in Gungahlin and the Constitution Avenue upgrade is another major factor," he said.

"The National Capital Authority and the ACT government are working together on upgrading Constitution Avenue now and they have already factored in public transport and lanes for cyclists.

"There is also a massive redevelopment going on in Campbell on the old horse paddocks and if you provide good public transport now, people who are moving in don't have the need to purchase two cars per family.

"This is something government should be looking at whenever they plan development, asking what is the public transport outcome."

As many as 520 dwellings are planned for the Campbell site, as well as mixed use buildings and a new park. Running services through the city's shopping district could also benefit consumers and residents, as well as students at Reid CIT.

Mr Haas said the inevitable extension of tram services over Lake Burley Griffin should be being considered by planners now.

"The extra money that is needed is minimal compared to other public transport options," he said. "You can leverage off the money you are already spending."

Effective use of light rail around the city could help grow tourism and budget travellers would be more likely to fly to Canberra if they could save on taxi or car hire prices.

Mr Haas called for Canberra Airport to contribute to a link from the city.

Expressions of interest from private consortium partners for the first stage city to Gungahlin route will close on December 19.