Population in the inner 100 sq km approx of six cities – Manhattan is the exception; it’s only 59 sq km, giving it a higher average density than central Paris

The Age editorialist reckons the $10 Billion Melbourne Metro rail tunnel now under construction is transformative infrastructure, but it’s not enough to deal with the city’s “congestion crisis” (Melbourne’s congestion crisis: The Metro rail tunnel is just not going to cut it):

A failure by successive Victorian and federal governments to adequately plan and to invest in public transport has created Melbourne’s most pressing and profound problem: congestion.

The writer thinks we should be dealing with congestion by building far more urban and regional public transport:

Multiple train line upgrades and extensions are needed… (The) ultimate solution to congestion is public transport.

The ultimate solution to traffic congestion is public transport, essentially rail? We certainly need to invest more in rail – a lot more – in order to handle projected population growth, but the solution requires more than that. Public transport is part of the solution but it can’t do it by itself:

  • Because building public transport infrastructure does not significantly reduce traffic congestion any more than building motorways does. The space vacated on roads by motorists who shift to the new train is soon taken up by other motorists i.e. induced demand.
  • Because the cost of retrofitting a public transport network that could attract all or even most travellers away from cars would be stratospheric. Paris has 303 stations within circa 5 km of the city centre; Melbourne has just 28 (see Can we build a metro just like the one Paris’s got?).
  • Because our cities are low density compared to the likes of successful transit-oriented cities such as Paris, Manhattan and London and we seem intent on keeping them that way. Paris has 2.25 million residents within the first 5 km; Melbourne has 430,000, most of whom resist higher densities (see How dense are our cities compared to Paris? and Is 16-storeys OK in the inner city?).
  • Because much larger and denser cities like Paris and Manhattan with outstanding rail networks are nevertheless still afflicted with serious traffic congestion. Drastically limiting car use is politically very hard in most places.
  • Because our multi-generational preference for private transport isn’t magically going to go away. Cars are currently much faster on average than public transport for all trips other than those to a few very dense places e.g. the CBD (see Is driving quicker than taking the train?). Autonomous cars promise to make driving even more convenient than at present (see What should we be doing now to prepare for driverless cars?). Electric vehicles powered by renewable energy sources will reduce significantly the environmental problems with cars (see Are electric cars a game-changer?).

The only way to tackle traffic congestion is to ration access to road space in some way. Some Chinese cities use odds and even number plate days without success; the obvious candidate is network congestion pricing. That can reduce the number of vehicles, increase average speed in the peak, and help make space for other road users like buses, trams and two-wheelers (see Is congestion charging just too unfair to bother with?).

The common argument is that congestion pricing can only be implemented if travellers have access to alternative public transport that’s as fast and convenient as driving. That condition would effectively rule road pricing out in Australian cities. However, it’s overly demanding; given driving is under-priced, there’s excessive car travel and hence no warrant for providing the same quantity of transit service. Moreover, motorists can shift the timing of trips to lower cost off-peak periods, or they can chain trips.

But reducing traffic congestion isn’t the only objective and arguably not even the main one; it’s a pity politicians and editorialists focus exclusively on it. The other key purpose is to increase access. New motorways eventually induce congestion at peak periods, but they increase the number of travellers who can get places, albeit slowly in the peak but faster in the off-peak. Public transport doesn’t “solve” traffic congestion either, but it excels at moving large numbers of people who want to go to the same place at the same time, albeit more slowly than driving in uncongested traffic.

If Melbourne really does grow at the projected rate (and that’s by no means certain), I think a number of key actions along the following broad lines are necessary:

  • Increase the supply and coordination of public transport; some new rail lines will be required but the weight of change must come from repurposing existing road space for high frequency buses and trams (see How can public transport work better in cities?).
  • Moderate demand by pricing access to the road network and encouraging vehicles to use motorways rather than high amenity streets. Given the scale of projected population growth, some increase in kilometres of motorway will likely be necessary.
  • Encourage a shift to more space-efficient private vehicles i.e. smaller, slower and kinder to others. The greatest promise is speed-limited electric scooters using dedicated road space. The priority shouldn’t be to eliminate all travel by private modes; it should be to eliminate large, fast, low-occupancy vehicles.
  • Require autonomous passenger vehicles to be shared (i.e. like a driverless taxi), powered by electricity, and charged by trip distance and time-of-day.
  • Reduce barriers to higher residential and employment densities in established suburbs, with greater intensity in locations close to high capacity public transport. Continue to permit well-planned incremental residential expansion at the fringe.

These actions should be supported by higher-level policy initiatives, especially shifting metro electricity generation to clean sources and removing taxation incentives that make housing as much about investment as shelter. The implementation would also vary spatially e.g. higher public transport mode share in denser areas; more private transport in less dense areas.

There are a few other claims in The Age’s editorial that I think warrant more explanation e.g. the idea that Melbourne Metro is “transformative”; and the charge that airport rail “has been forced off the agenda because of surging demand on the Sunbury and Melton lines”. The one I want to comment briefly on though is the claim that:

Evolving technologies will help ease Melbourne’s growing pains – ride sharing and driverless cars will probably reduce gridlock.

If they’re implemented on the current model of private car ownership – i.e. business as usual – I think it’s far more likely driverless cars will increase gridlock, not reduce it. That’s because they’ll significantly reduce the cost of travel. If you send your driverless vehicle up to the automated dispenser to pick up groceries while you sleep in, you probably don’t care too much if it sits in congested traffic for 30 minutes longer than it would off-peak.