On face value the two issues appear unrelated, but many Canberrans reading of the staggering potential cost of light rail stage two will find it difficult to separate it from the unwelcome increases many are this week facing in their rates bills.

ACT Transport Minister Meeghan Fitzharris is unhappy the Federal Parliament's joint standing committee's apparent insistence on a light rail route that crosses the Kings Avenue bridge would increase the spend by around $300 million.

Her government, responding to questions on notice, said this could push the price up to an eye-watering $1.9 billion. The Commonwealth Avenue bridge route would come in around $1.6 billion.

Both figures are staggering given many Canberrans seem poised on the verge of a rates revolt and even the ACT Greens, the group often blamed for the light rail push, are concerned about fairness and equity in the way rates are calculated.

The party has released a discussion paper espousing the use of a capital investment value or improved capital value system as an alternative to the existing average unimproved value method of setting rates.

The current system, according to former Treasurer Ted Quinlan, has pushed the owners of small units in large complexes into the highest rating brackets with the owners of one such property telling Fairfax their rates and land tax bills now totalled $4,300 a year.

The problems are not confined to units. One investment property owner told The Canberra Times it takes more than 19 weeks of rental income to cover a rates and land tax bill of almost $10,000 a year.

While it is not strictly correct to state, as many light rail critics often do, there is a direct correlation between this project and the rate increases giving Canberrans bad cases of "sticker shock" every time they get their latest assessment, the issues aren't entirely separate either.

If, as Fitzharris fears, the cost of the Woden light rail service blows out by $300 million because of the need to use Kings Avenue, that shortfall would have to be made good by the city's property owners.

The threat the Barr Government would likely walk away from stage two in this event may be the best bit of news some Canberrans will have heard in years.

While $1.9 billion appears definitely out of the question, there are many who would argue a projected $1.6 billion spend can't be justified either. It's worth remembering the current expected bill for stage one from Gungahlin is well north of what was initially estimated and sold to ratepayers.

Stage one does make some sense. Gungahlin is the city's fastest growing precinct; there have been additional benefits flowing from the reinvention of Northbourne Avenue and Canberra's gateway and there is the possibility of an extension to Russell further down the track.

While only time will tell if these benefits justify the investment, the case for stage two is far more marginal.

According to the ACT Government $1.9 billion is too much to spend on the Woden line. It now needs to produce the detailed business case to prove that the same can't be said of the $1.6 billion.