Some things we do know. HSR is expensive. It takes a long time to build. It is the gaudiest jewel in the urbanist’s crown and the symbol of engineering madness to believers in small government and low taxes. Melbourne to Sydney is the world’s fourth busiest air traffic corridor. The cities of 5 million are separated by about 730 kilometres of mostly rail-friendly terrain – by coincidence, the distance at which total travel time by HSR and plane is about the same. Air travel for most of us is a dreary, cramped affair, while a journey on a good train is a marvel. So what’s standing in the way? One obstacle is incomplete accounting. The studies stick quite narrowly to the economics of moving people and goods from A to B. Even if one accepts that over the long term HSR would pay for itself with competitive fares and divert a great deal of demand from airports, it is reasonable to ask what problem it is intended to solve. It wouldn’t save time, it couldn’t be a whole lot cheaper given the fiercely competitive airline prices, and going station to station by aviation is hard-wired into the national psyche. The transportation platform is not on fire. Prime Minister Malcolm Turnbull announced funding for an airport rail link last month . Credit:AAP But there is another burning platform: metropolitan sprawl and Melbourne’s imminent overtaking of Sydney in total population. Neither city’s residents seem buoyed by the projected 8 million population by 2050. Absorbing 100,000 new people a year gobbles up agricultural land, strains infrastructure, and creates a febrile real estate market. My impression is that most Melburnians and Sydneysiders find this unsettling.

The Economist Intelligence Unit annually and famously rates Melbourne as the world’s most liveable city. (Other similar rankings have it lower down but still high.) The top tier belongs mainly to smaller cities like Auckland and Stockholm and Dusseldorf and Vancouver. Melbourne, Sydney and Toronto are by some margin the biggest highly-ranked cities, and no urban area with 10 million or more ever cracks the elite group. Cities outgrow their liveability and appear never to get it back. That is the future towards which Melbourne and Sydney are headed unless the growth can be decanted elsewhere. That inevitability is the strongest case for HSR. A Melbourne-to-Sydney link makes it possible to create and sustain “suburbs” 200 kilometres from either city. Land and housing would be cheaper. There would be opportunities for highly skilled people who prefer smaller places. Australians would inhabit more of their vast territory. The line would grow an economic corridor that opened up new possibilities along the way and on either side. Loading Replay Replay video Play video Play video In the end HSR may not be enough to put a dent in the projections even if it could be built in a miraculously short period of time. Throughout the world people flock to enormous cities where hopes are high and misery ubiquitous. But HSR has a better chance than hand-wringing and nostalgia. Absent HSR it is difficult to imagine a scenario where both cities are not ultimately done in by their own success. They already support great universities, excellent art galleries, thriving cultural communities, and first class sports and entertainment. The bounty from the next few million will include more congestion, new levels of real estate hyperventilation, and communities of solitudes defined by economic class.