Beyond "peak car": Why Australia's traffic projections are almost certainly wrong

Rush hour traffic in Melbourne. Image: Getty.

Most mathematical modelling used to guide our economy is simplified and only modified when it becomes so out of touch that it is dangerous. When the Atlantic cod fishery collapsed, the model being used to set fishing quotas was still suggesting the fishery was healthy. In retrospect it seems a kind of madness to have kept using it.

Traffic modelling in Australia is now similarly out of touch. A recent study by the Bureau of Transport Industry & Resource Economics modelled the future of traffic in Australian cities. If it had been a mere academic study it would not be dangerous, but it is now being used to justify massive road spending.

The report suggests that travel times will blow out and road congestion will cost the economy more than A$50 billion. Congestion, it seems, is out of control and will engulf us all, with terrible economic consequences for Australian cities.

Modelling relies on heroic growth assumptions

In order to reach these numbers the report had to make assumptions about growth trends in car use per capita. The high-growth scenario is included in the red box below.

Traffic modelling shows a sudden reversal in car use from the clear trend in Australian cities over the past decade. image: BITRE/author provided.

As is common in such modelling, a low-growth scenario is also modelled and then the future is taken to be in the middle.

The high-growth scenario can be seen to reverse a trend in car use per capita that appeared to be well set after a peak in 2003-04. This peak car phenomenon has been found in all developed cities, and has been analysed by many commentators including ourselves.

Understanding the peak car phenomenon would appear to be a basic requirement before attempting future scenarios that wipe it out completely. However, this report has not ventured into such questions. Instead, it continues the methodology used for the past 30 years.

Travel time reality means car use has peaked

The fundamental problem is that the model does not understand how cities work. Travel time is seen as something that just expands as our cities of car-dependent suburbs grow outwards.

However, the Marchetti travel time budget of just over an hour on average has been found to apply universally across all cities. Some people can go beyond an hour and some much less, but the average everywhere is an hour. This has been found over and over to apply in every city.

If people find it hard to live with so much time “wasted”, they move to somewhere more within their travel time budget. If the overall options in housing, jobs and travel become so dysfunctional that people are forced to travel beyond their time budget then the issue becomes highly political: elections are fought over infrastructure and housing options. Cities adjust; they don’t keep expanding travel time.

It is possible to understand the global peak car phenomenon in terms of cities hitting the Marchetti wall. In our data, cities everywhere began to grow in their traffic congestion whether or not they built freeways or extra road capacity. This was because these just filled very quickly.

Rail projects unclog the urban arteries

Rail projects, however, could go around, over or under the traffic. Hence, over the past 30 years, rail lines have become more travel-time-efficient than traffic arteries. Many people, especially the young and wealthy, began to move back into areas where public transport was well provided.

The rejuvenation of central and inner areas is not just because they are cool and trendy, but because they offer reduced travel time. Car use per capita goes down when there is less need to travel, especially by car.

With fixed road capacity, traffic volumes stay constant

This model does not consider this to be significant enough to consider in forecasting scenarios for Australian cities. It crudely projects a totally car-based-and-growing set of futures. It barely considers the remarkable global turnaround in the building of rail systems and the rejuvenation of cities.

Scenarios where these urban trends are considered to continue (rather than suddenly dying as suggested bythe chart above, followed by inevitable growth in car use) would make much more sense. This is the way planning is being done in cities like London.

The evidence in London and other cities – with good public transport alternatives and competitive door-to-door journey times – is that, with fixed road capacity, traffic volumes stay constant (or slightly decline). All the growth goes on to public transport and the car-based share of travel falls – down from 46 per cent for residents of London in the 1990s to 32 per cent now.

The scenarios for London are therefore all about how best to build public transport and land-use options that can enable economic growth to occur sustainably, rather than trying to increase road capacity. Similar considerations can be seen to be happening elsewhere around the world.

Did an ‘Abbott effect’ skew the modelling?

The modelling work dates back to when prime minister Tony Abbott was all about building roads and wouldn’t fund rail. Image: AAP/Dan Himbrechts.

So why have we in Australia refused to change our modelling and are still trying to justify massive road capacity increases?

Traffic modelling reports like this take about two years to produce. What was happening around two years ago was the election of Tony Abbott with his commitment to spend some A$40 billion on urban roads and nothing on urban rail.

Huge road projects in Melbourne (East-West Link), Sydney (West Connex), Brisbane (Gateway) and Perth (Freight Link) were all announced before any assessment. Their rationale was very shaky and most of these projects have now either failed or are failing.

Each road project also has large impacts on their urban economies. These are dangerous as they destroy so much of the urban fabric necessary for rejuvenation and take away the ability of governments to pay for the more important urban rail projects on their agendas.

The upturn in the graphs in Figure 1 seems to be an Abbott effect. It is rather amusing now that this report came out just as Malcolm Turnbull took over and began talking up urban rail and urban regeneration.

Such models should be put into the museum and as a better sense of where our cities can be going. This report can be easily passed over – but if the thinking behind it stays, the impact on our cities will be very damaging.The Conversation

Peter Newman professor of sustainability Curtin University

This article was originally published on The Conversation. Read the original article.


Covid-19 is highlighting cities' unequal access to green space

In the UK, Londoners are most likely to rely on their local park for green space, and have the best access to parks. (Leon Neal/Getty Images)

As coronavirus lockdowns ease, people are flooding back to parks – but not everyone has easy access to green space in their city.

Statistics from Google show that park attendance in countries across the globe has shot up as people have been allowed to move around their cities again.

This is especially true in urban areas, where densely populated neighbourhoods limit the size of private green space – meaning residents have to go to the park to get in touch with nature. Readers from England can use our interactive tool below to find out how much green space people have access to in their area, and how it compares to the rest of the country.


Prime Minister Boris Johnson’s announcement Monday that people are allowed to mingle in parks and gardens with groups of up to six people was partially following what people were doing already.

Data from mobile phones show people have been returning to parks across the UK, and also across Europe, as weather improves and lockdown eases.

People have been returning to parks across the world

Stay-at-home requirements were eased in Italy on 4 May, which led to a flood of people returning to parks.

France eased restrictions on 1 May, and the UK eased up slightly on 13 May, allowing people to sit down in public places so long as they remain socially distanced.

Other countries have seen park attendance rise without major easing of lockdown – including Canada, Spain, and the US (although states there have individual rules and some have eased restrictions).

In some countries, people never really stopped going to parks.

Authorities in the Netherlands and Germany were not as strict as other countries about their citizens visiting local parks during lockdown, while Sweden has famously been avoiding placing many restrictions on people’s daily lives.

There is a growing body of evidence to suggest that access to green space has major benefits for public health.

A recent study by researchers at the University of Exeter found that spending time in the garden is linked to similar benefits for health and wellbeing as living in wealthy areas.

People with access to a private garden also had higher psychological wellbeing, and those with an outdoor space such as a yard were more likely to meet physical activity guidelines than those without access to outdoor space. 

Separate UK research has found that living with a regular view of a green space provides health benefits worth £300 per person per year.

Access is not shared equally, however, which has important implications for equality under lockdown, and the spread of disease.

Statistics from the UK show that one in eight households has no garden, making access to parks more important.

There is a geographic inequality here. Londoners, who have the least access to private gardens, are most likely to rely on their local park for green space, and have the best access to parks. 

However the high population in the capital means that on the whole, green space per person is lower – an issue for people living in densely populated cities everywhere.

There is also an occupational inequality.

Those on low pay – including in what are statistically classed as “semi-skilled” and “unskilled” manual occupations, casual workers and those who are unemployed – are almost three times as likely as those in managerial, administrative, professional occupations to be without a garden, meaning they rely more heavily on their local park.

Britain’s parks and fields are also at significant risk of development, according to new research by the Fields in Trust charity, which shows the number of people living further than a 10-minute walk from a public park rising by 5% over the next five years. That loss of green spaces is likely to impact disadvantaged communities the most, the researchers say.

This is borne out by looking at the parts of the country that have private gardens.

The least deprived areas have the largest gardens

Though the relationship is not crystal clear, it shows at the top end: Those living in the least deprived areas have the largest private green space.

Although the risk of catching coronavirus is lower outdoors, spending time in parks among other people is undoubtedly more risky when it comes to transmitting or catching the virus than spending time in your own outdoor space. 

Access to green space is therefore another example – along with the ability to work from home and death rates – of how the burden of the pandemic has not been equally shouldered by all.

Michael Goodier is a data reporter at New Statesman Media Group, and Josh Rayman is a graphics and data visualisation developer at New Statesman Media Group.