Mr Coe posed with two loaned Audi A3s outside the entrance to Exhibition Park on Flemington Road to demonstrate what he said was an unreasonably high cost to the taxpayer for the 12 kilometre tram route.

"When you are talking in such massive numbers, it is difficult to comprehend what it means," Mr Coe said.

"What this exercise is all about is trying to put [the cost] into units that people can understand. The cost of construction would buy 18,000 Audi A3 convertibles, one for every household in Gungahlin, demonstrates the enormity of the project."

The ACT Government believes the tram will reduce road congestion, activate the Northbourne Avenue corridor and create as much as $1 billion in benefits for Canberra. The project's final business case, released on October 31 by Capital Metro Minister Simon Corbell, found a return of $1.20 for every dollar spent.

Mr Coe and the Canberra Liberals have pledged to stop construction of a wider light rail network if they win the 2016 election, but have so far stopped short of saying an incoming Liberal government would tear up existing contracts or demolish already constructed infrastructure.

"I don't think there will be many people in Canberra who will think that we are announcing a policy here to procure 18,000 Audis, but if constituents want to write to us advocating for that policy we'll hear them out," Mr Coe said.

"The point is to simply show how serious a commitment this light rail line is and exactly what the opportunity cost is as well."

Mr Coe said evidence for the line's value remained contested, and tram services could simply shift passengers from existing bus routes linking the city and Gungahlin.

Construction is due to start in 2016, with services running on the line by 2019.

The business case said drivers would save 15 minutes travel time in 2031 because of tram services, with an expected daily patronage of 13,700 in the first year and 20,700 by 2031.

He said the opposition's public transport policy could be released as soon as next year.

"We are doing a lot of work with regard to the operational side of buses and the infrastructure side of transport, whether it be bus priority measures on Northbourne Avenue and elsewhere and whether we can improve the efficiency of car traffic as well.

"Certainly next year we will be discussing and outlining plans for Northbourne Avenue. I think Canberrans have an interest and a right to know what the alternative to light rail is."

Expressions of interest from potential business consortium partners close on Friday.