Note explaining Automobile dependence, peak car use and induced traffic

Automobile Dependence

The situation where our choices and ability to move around the city are constrained by our access to a car, and where ‘use of an automobile [becomes] not so much a choice but a necessity’ (Newman & Kenworthy, 1999, p. 32).
Good sources for more information on automobile dependence’s causes and implications for cities are Newman and Kenworthy’s (1989) book Cities and automobile dependence and the website

Peak car use

Though most cities around the world have demonstrated some level of car dependence over the last fifty-plus years, growth in car use in Australia and other developed countries peaked in 2004 and is now decreasing in a trend known as ‘peak car use’ (Newman & Kenworthy, 2015). As both a cause and result of this trend is the fact that cities are no longer being planned solely around the automobile (Newman & Kenworthy, 2015, p. 5). Newman and Kenworthy (2011, pp. 33-37) discuss six potential causes for this trend:

People are generally willing to ‘budget’ for one hour of travel per day

The ‘Marchetti constant’ (Marchetti, 1994; Newman & Kenworthy, 1999) suggests that when our cities become ‘one hour wide’ (Newman & Kenworthy, 2011), or about 50km wide given average car speeds of 50km/h, further expansion beyond this limit becomes less attractive and traffic becomes a problem within these limits, because the time we are generally willing to spend travelling each day is exceeded. Thus, we see cities slow in their expansion, public transport becomes an attractive way to avoid traffic, and locations closer to destinations become preferable.

Public transport is increasing in popularity

This trend is due to a number of reasons, not least the high cost of owning and running a car, and preferences for people, especially younger generations, to use their commute times to do other things than drive (for instance reading and using their devices for any range of activities).

The reversal of urban sprawl

Densities in cities are increasing comparatively to rates of sprawl due to consumer preferences and government policies. Less sprawl and more people living closer together and closer to places they want to go leads to reduced reliance on cars to do so.

The ageing of cities

Many cities in developed countries are experiencing a rise in the average age of their citizens, and on average people drive less as they get older.

The growth of a culture of urbanism

As young people moving out of family homes, older people are moving back towards city centres from suburbs, as young people too are showing a preference for inner-city life over suburban life, and for other forms of technology over cars.

The rise in fuel prices

Given relatively high fuel costs and price instability, the ownership of a car and its regular use becomes increasingly expensive and decreasingly appealing.

So what does this mean for Sydney?

Sydney is already greater than ‘one hour’ wide (Penrith is 70km from the CBD by car), public transport is increasingly popular (90% of western Sydney commuters into the CBD come by public transport already) (SGS, 2015), the city is densifying, renewing and reducing the rate at which it sprawls (consider urban renewal projects proximate to the CBD such as at the bays precinct and Green Square), Sydney’s average age is increasing along with Australia and most other developed countries, there is a strong culture of urbanism (such as increasing consumer preferences to live within walking distance of ‘centres’ such as Parramatta) and fuel prices (and toll costs) that continue to impact car owners, especially those with the least ability to afford it.

Sydney is not on a different path to other cities of the developed world. It too is in the middle of ‘peak car’, meaning that the need exists to reprioritise infrastructure provision to reflect and adapt to this trend.

Induced traffic

Induced traffic occurs when congested motorways increase in capacity (Zeibots, 2007). This increased capacity leads to faster travel times initially, though also gives people more time to travel further by car (as they spend less time travelling on their original trip—and given our travel budgets of up to an hour a day) and also increases appeal for others to either swap travel mode (eg swapping from public transport to car after a motorway expansion) or to create new journeys by car themselves. The ‘induced’ demand, this creation of new trips and new users of the roadway, ensures that ‘congestion-busting’ efforts that rely on expanded road capacity are ineffective and is the major reason that even the most traditionally car-dependent cities are turning to alternatives for transportation (such as light rail projects in Phoenix, Dallas and LA, see
For an easy to read look at induced traffic, see: .

The relationship between peak car and induced traffic—could they happen at the same time in Sydney?

Yes. Peak car is a global occurrence especially common in developed nations. We saw peak car use in Australia in 2004, when the rate of increase in automobile use slowed, and it is a trend that will continue given the other associated societal trends listed above. On the other hand induced traffic relates to location-specific expansions in road capacity. So Sydney certainly could be exhibiting an overall peak in car use while at the same time drivers and everyone else suffer from government decisions that directly lead to more traffic.


Marchetti, C. (1994). Anthropoligical invariants in travel behaviour. Technical Forecasting and Social Change, 47(1), 75-78.

Newman, P., & Kenworthy, J. (1989). Cities and automobile dependence: An international sourcebook. Aldershot: Gower Publishing.

Newman, P., & Kenworthy, J. (1999). Sustainability and cities: Overcoming automobile dependence. Washington, D.C.: Island Press.

Newman, P., & Kenworthy, J. (2011). ‘Peak car use’: Understanding the demise of automobile dependence. World Transport Policy and Practice, 17(2), 31-45.

Newman, P., & Kenworthy, J. (2015). The end of automobile dependence: How cities are moving beyond car-based planning. Washington, DC, USA: Island Press.

SGS. (2015). Strategic review of the WestConnex proposal: Final report. Sydney: SGS Econimics and Planning.

Zeibots, M. E. (2007). Space, time, economics and asphalt: An investigation of induced traffic growth caused by urban motorway expansion and the implications it has for the sustainability of cities. (Doctor of Philosophy in Sustainable Futures), University of Technology, Sydney, Sydney.   

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