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The logic, or illogic, of light rail in Canberra

Remember geometry proofs? One would set up axioms that were said to be incontrovertible ("If two sides of a triangle are congruent …") and then make inferences based on those axioms to come up with hopefully sound logical conclusions ("... then the angles opposite those sides are congruent."). Old-fashioned types would finish any argument off with "QED", Latin for "quod erat demonstrandum": "which is what had to be shown".

There has been a flurry of argument around light rail in Canberra. But unlike the relative certainties of geometry, this real world project is not nearly so definite and neither are the various "proofs" being offered around it. Nonetheless greater clarity may be possible by putting out relatively solid "axioms" and then considering reasonable conclusions that might be drawn from them.

One axiom appears to be very solid, bearing the preponderance of evidence behind it:

1. Current ACT transit service + current ACT mode share using transit (ie, percentage of trips using transit) + projected ACT population growth and development = future traffic congestion and auto emissions.

The evidence is clear that the ACT needs to reduce automobile traffic given expected growth and there is now bipartisan political agreement on this point. A reasonable logical inference therefore says we need (a) to increase transit alternatives and (b) transit usage rates to avoid future congestion and environmental costs. QED.

How we do accomplish (a) and (b) above? Things get trickier here, but I would offer two more strong axioms, also having weight of available evidence behind them, that can move the logic further along:

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2. The Canberra light rail project as currently conceived (a) does not deliver sufficient transport benefits (ie, travel time reductions per traveller vs current alternatives, including buses), to yield a positive net gain to the ACT but, (b) may yield a total net gain when land development caused by light rail is added to the calculation.

3. Buses (a) deliver transport benefits at lower cost than light rail but (b) deliver less economic development benefit than light rail.

The evidence behind these two axioms is quite clear. Analyses, most recently from the ACT Auditor-General and going back to the government's own business case for the project does indeed show that it is the development potential of light rail, added to its transport benefits, that push it over the net gain line. These and other analyses show that buses deliver transport benefits significantly more cheaply than light rail but provide less development impact. QED.

From this point, what can be proved by logic and "axiomatic" fact reaches its limits and the debate now is really about political and social values. Light rail is seen by some as offering superior traveller amenity, more permanence, more attractiveness to property developers and more potential for urban transformation and if these are highly valued, light rail is worth the cost.

Bus advocates focus on bang for buck and relative timeliness in delivering greater transit penetration and uptake (by no means fully concede amenity and development potential especially since bus technology is improving) and value achievement of these goals more highly than longer-run urban development. These positions need not be inconsistent, of course.

It is possible, for example, to believe that transit usage should first be boosted by better bus service, with light rail to follow when sufficient densities and growth are achieved. But here too the arguments turn more on belief about what is more or less important and more or less valuable. These differences cannot be reconciled purely logically or even empirically.

Prima facie arguments as to the suitability of light rail as a transport investment do not really work to bridge these differences. For example, some have said that cities as small as Canberra have light rail. Therefore Canberra should. Yes, but cities larger than Canberra do not have any rail, eg, Bogota, Colombia (over 8 million people), which use Bus Rapid Transit (BRT) to achieve tram-like outcomes. Similarly, arguing that Canberra is wealthy enough to afford light rail and therefore should invest in it can be set against the argument that buses are cheaper and one could build a much more extensive bus system on a current light rail budget, leaving resources left over for other things.

Indeed, reasonable people can and do reasonably disagree about whether Canberra should have a tram or not and people do have different value judgments in these matters. It is now up to the voters to draw the conclusions they want for Canberra. After October 15, we'll see what those are and go from there. QED.

Dr Cameron Gordon is an adjunct associate professor at the University of Canberra Health Research Institute and lecturer at the Research School of Economics at the ANU.