The Commonweath’s new Phase 2 report on high-speed rail forecasts that if HSR is built on the east coast, total emissions from travel in the corridor over the 50-year evaluation period would be 384 million tonnes (Mt CO2-e). But in the base case, which assumes HSR isn’t built, emissions would total 362 Mt CO2-e. That’s 22 million tonnes less than under the HSR scenario …

Change in GHG emissions arising from the operation of HSR relative to the Base Case (Mt CO2-e). Source: Phase 2 HSR Report

It’s not that travelling by HSR isn’t greener than flying or driving. Attracting around half of all airplane travellers in the corridor to HSR would reduce emissions from aviation by 116 Mt CO2-e over the period. There’d also be a further saving of 11 Mt CO2-e from travellers who shifted from cars, coaches and conventional trains to HSR.

On the other side of the ledger, though, HSR itself would emit 35 Mt CO2-e in operation over the 50-year period and a further 11 Mt CO2-e during construction. Also, based on experience with HSR in other countries, the study reckons there’d be an additional 21 Mt CO2-e due to “induced” travel — that is, additional trips that would’t otherwise have been made but for the improvements in accessibility provided by the HSR network.

That still has HSR ahead, although not by as much as many imagine. Total emissions under the HSR scenario would be 303 Mt CO2-e, compared with 362 Mt CO2-e in the base case.

Now here comes the really interesting and potentially controversial part: suppressed demand. The base case assumes there would be no increase in aviation capacity in Sydney over the evaluation period — so no second Sydney airport and no expansion of Kingsford Smith. That means there’d be a growing level of suppressed demand for air travel between Sydney and other destinations in Australia and overseas.

However, under the HSR scenario, all those Sydney air travellers who change over to bullet trains would release spare capacity at Kingsford Smith airport.