Patrick Moriartya, 
, 
and Damon Honneryb
aDepartment of Mechanical Engineering, Monash University, P.O. Box 197, Caulfield East 3145, Vic., Australia
bDepartment of Mechanical Engineering, Monash University, P.O. Box 31, 3800 Vic., Australia
Available online 22 July 2008.
Abstract
Nearly all researchers into the future of global passenger transport assume that both car-ownership and overall vehicular travel will continue to rise. But they also increasingly acknowledge the environmental and resource problems facing vehicular transport, particularly global climate change and oil depletion. In order to meet these challenges, researchers propose a variety of technological solutions, including greatly improved vehicular fuel efficiency, alternative fuels and propulsion systems, and carbon capture and storage. In this paper we question whether these optimistic solutions can be developed and widely deployed in the limited time frame available, and argue instead that not only are ever-rising vehicular mobility levels unlikely to occur, but that the human costs of continuing this approach are also too great. Instead we argue that because transport is a derived demand, we must first articulate a preferred vision of the future, then design an appropriate, sustainable transport system. Finally, we briefly outline what such a low-mobility future transport system would look like, using our own city, Melbourne, Australia, as a case study.
Article Outline
1. Introduction: forecasting global passenger travel
Global passenger transport has risen steeply over the 20th century; in the year 2000, total vehicular travel worldwide was estimated as about 32 trillion passenger-km (tkm), up from only 2.8 tkm in 1950 [1] and [2]. Presently, most global passenger travel is by car, although air travel is increasing its share. Schafer and Victor [3] have projected global vehicular travel out to the year 2050. They consider travel to be constrained only by individual time expenditure and household budgetary outlays. They claim that, worldwide, travel time (including that for non-motorised travel) is roughly constant at about 1.1 h per person per day, and that at least for countries with levels of car ownership at 0.2 cars/capita and higher, households limit transport expenditures to around 10–15% of household income. With additional assumptions – chiefly on future global income growth – future travel levels and their split between high-speed (air and rapid rail) and other modes can be calculated. By 2050 they project a total of 103 tkm travel, with high-speed modes and car travel accounting for close to 80%. Although they see some bridging of the gap between high- and low-travel countries, travel is also projected to grow strongly even in the already high-mobility OECD countries.Other recent studies have also forecast greatly expanded vehicular travel for the 21st century. Ausubel and Marchetti [4] again project vehicular travel as growing strongly within travel time and income constraints, but regard underground magnetically levitated (maglev) trains running at very high speeds in evacuated tunnels as the major travel mode of the future. Unlike Schafer and Victor, they explicitly recognise the need to reduce transport greenhouse gas emissions. They regard ever-rising vehicular mobility as a fundamental human desire, rather than as a derived demand for access. The airline manufacturer Airbus [5] annually issues single value forecasts 20 years ahead for world air travel. Their latest projection assumes that air passenger travel will grow annually by 4.8% out to 2025, with much of the growth from newly industrialising India and China, where air travel is already growing strongly.
Recently, a number of reports, some from official agencies, have appeared on the future of global transport (e.g. [6], [7] and [8]). Like most recent research on future transport, but unlike the research just discussed, these reports do not rely on single figure projections. Instead, they make extensive use of scenarios which are presumably meant to bracket the range of possible transport futures. Nevertheless the reference scenarios all foresee rising travel levels. Although these studies recognise the challenges posed by global oil depletion and climate change, the emphasis is solely on technological solutions capable of being integrated with the existing transport system. What is lacking is an explicit discussion of a preferred future, or a full examination of the human consequences of their scenarios. The possibility of a lower-mobility future is not even considered. In the useful terms of Borjeson et al. [9], their scenarios are ‘preserving’ rather than ‘transforming’. Major changes are seen as possible in the technological system, but existing social/economic systems are implicitly assumed to be immutable.
We are sceptical that the technological measures needed for these projected high-mobility futures can be implemented, particularly given the limited time frames available. This paper accordingly first looks at the constraints, both technical and economic, that confront ever-expanding vehicular passenger mobility, and concludes that such a transport future would require both extraordinary effort and a number of major technical breakthroughs. It then assesses whether such an effort, which is probably doomed to fail, is worth undertaking in the light of the high human and environmental costs already apparent in the global transport system-costs that can only expand as the transport system grows. Finally, we argue for a more egalitarian and environmentally sustainable future, and briefly outline what a transport system for such a future would look like, using our own city, Melbourne, Australia, as a case study.
2. Future constraints on high-mobility global travel
Futurists often distinguish between possible, probable and preferred futures [10] and [11]. Here we look closely at what is possible and probable for future passenger transport, using a constraints approach. Although for transport, only the physically impossible can be ruled out with certainty (e.g. faster than light travel), a number of more subtle constraints will act and their combined effects need to be considered. In recent years, as the twin challenges of global oil depletion and global climate change have been increasingly recognised, a vast literature has emerged which examines technical solutions to the constraints that result from these problems. Even in the recently released Intergovermental Panel on Climate Change (IPCC) report [8], the emphasis on emission reductions for transport is almost entirely on such technological fixes. The main direct approaches have been to advocate increased fuel efficiency, and alternative fuels and power systems for vehicles. The leading indirect approach for addressing global climate change effects of fossil fuel use in general is carbon capture and storage, but recently, a number of papers on geo-engineering (the intentional modification of global climate) have appeared. Of course, neither of these indirect solutions can address the oil depletion challenge. This section first looks at the two main environmental/resource challenges facing high-mobility transport, together with the proposed tech fixes, then examines transport's possible future economic problems.
2.1. Possible technical constraints
Today, despite the growth of biomass fuels, petroleum-based fuels still account for 98% of transport fuel [12]. Further, the share of oil used for transport oil has steadily increased over the past three decades. The reference cases for the Energy Information Administration (EIA) and International Energy Agency (IEA) both project that world demand for oil (both conventional and non-conventional) in 2030 will have risen to 117–118 million barrels per day (mbd), compared with around 84 mbd in 2006 [12], [13] and [14]. Evidently, these organisations expect oil to remain the dominant transport fuel in the future. But the Association for the Study of Peak Oil and Gas (ASPO)-whose key members are retired petroleum geologists-argues that global oil production could peak as early as 2011, and that by 2030 will have fallen to only about 60 mbd [15].
This disparity in annual production/consumption forecasts arises because estimates for ultimately recoverable reserves vary widely [15] and [16]. Although the petroleum reserve estimates of BP and the production projections of the EIA and IEA still represent the mainstream view, the ASPO position is gaining support. There is, for example, growing appreciation that new annual discoveries are only replacing a fraction of annual oil use, and that OPEC oil reserves figures may be seriously inflated [15]. Great hopes are placed on unconventional oils, particularly tar sands, but these already have serious local environmental impacts. And compared with conventional oils, per litre of delivered fuel, these have much greater emissions of greenhouse gases (GHGs) [16], another challenge to sustainable transport.
In order to avert dangerous climatic change, the European Union recently proposed that global temperature increases should be limited to 2 °C above pre-industrial values [17]. The recent IPCC study implicitly supports this figure, indicating that serious adverse consequences will occur for such a temperature rise [18]. The IPCC also suggest that in order to limit increases to this value, carbon dioxide (CO2) atmospheric concentrations must be kept to 350–400 parts per million (ppm) or roughly at present CO2 concentrations of about 380 ppm [19]. They further show that the required reductions in CO2 emissions in 2050 are as high as 85% of the 2000 emissions and, of course, would be an even higher share of the larger 2007 emissions.
Climate change is unlikely to occur in a predictable, linear fashion. Overbeck and Cole [20], on the basis of paleoclimatic records, warn that abrupt change is the norm, rather than the smooth changes implicitly underlying most present discussions about climate policy. Nor is abrupt change merely a problem for the distant future. They state that ‘The potential for abrupt future change argues that we are already courting “dangerous anthropogenic interference” with the climate system.’ Even if climate change itself occurs in a gradual manner, the response of ecosystems may not, because like climate, they may have alternative stable states. Thus ‘gradual changes in temperature or other factors might have little effect until a threshold is reached at which a large shift occurs that might be difficult to reverse’ [21]. These ecological changes could compound the difficulty of dealing with climate change.
Some researchers feel that the most serious challenge posed by climate change is the abrupt rise in sea level from melting icecaps (e.g. [22] and [23]). They argue that the estimates given for 21st century sea level rise in the latest IPCC report do not give sufficient weight to very recent data showing much more rapid melting than currently used models can explain. James Hansen, a prominent climate modeller, states: ‘I find it almost inconceivable that “business as usual” climate change will not result in a rise in sea level measured in metres within a century’ [22]. The paleo-climatic record indicates that such rates of sea level rise have happened in the past. He adds that the growth of ice sheets like the Greenland icecap takes millenia, but that their disintegration can proceed very rapidly, because of multiple positive feedbacks. Evidently, avoiding adverse climate change and an irreversible commitment to large future sea level rises will require massive reductions in releases of CO2 and other greenhouse gases within a decade or two.
Countries like India and China are unlikely to agree to permanently lower annual per capita emissions than the OECD countries. Under the proposed ‘contract and converge’ system, all countries would converge on a common low per capita annual CO2 emissions figure over the next few decades [17]. Since the average OECD country per capita emissions of CO2 from energy use are today several times the global average (e.g. 4.7 for the US, 4.2 for Australia) [12], the reductions required are obviously major. A global 85% reduction by 2050 would need a more than 30-fold cut in US emissions under an equal per capita emissions policy. If transport sector reductions had to match those of the economy overall, then for the US, a similar reduction would be needed by 2050, and perhaps half this (i.e.15-fold) by 2030. Further, since US transport fuel use is forecast to rise by 41% from its present value by 2030 [13], a 21-fold cut would be needed, based on projected 2030 emissions. The only technical means for achieving these reductions are one or more of the following: improvements to vehicle efficiency, use of low-carbon transport fuels, carbon capture with sequestration, or geo-engineering.
A recent Swedish study suggested that at constant occupancy rates and speeds, fleet average passenger car efficiency might be raised 3–4-fold by 2050, mainly by shifting to hybrid vehicles. For public transport vehicles and aircraft, potential fuel efficiency improvements were much lower. By 2030, possible gains are smaller, probably only a 2–2.5-fold improvement for cars [24]. Even these potential gains from car engine improvements will be off-set by the declining occupancy rates that inevitably seem to follow rising car ownership, by decreases in ‘well-to-tank’ fuel efficiency as we move to unconventional oil sources, and by any further rises in auxiliary power requirements or vehicle size [17]. Indeed, modern Ford cars are no more fuel efficient than the T-model Ford [25]. Clearly, improvements to vehicle efficiency will not help much if very large emission reductions are needed.
What about alternative transport fuels? For the past two decades, despite the recognition of low-carbon energy as a potential solution to global warming, its share of world primary energy use has steadily fallen [12]. Even with supporting policies, official reports agree that it will be difficult to raise its share much beyond its present level by 2030 [6], [12], [13] and [16]. Part of the reason for its slow growth is higher than expected costs. Hultman and Koomey [26] have studied the ‘risk of surprise’ in the estimation of costs for energy technologies, especially nuclear energy in the US, and find that estimates are systematically over-confident in their assessment of future costs and construction times. They note that cost surprises are so pervasive for new energy technology that they should not really be considered as surprises, that over-confidence should be factored into estimates of future costs. The favoured alternative fuels for transport are presently biofuels; these are considered in the following section.
An earlier IPCC report, while optimistic about the prospects for carbon capture and sequestration, forecast that only 20–40% of all fossil fuel emissions would be ‘technically suitable for capture’ by 2050 [27]. By 2030, the 2007 IPCC report expects its contribution to be negligible [16]. One problem is that the energy expenditure is much greater if CO2 collection technology is added onto existing fossil-fuelled plants rather than built into new plant; a 2001 US study found that capturing 96% of CO2 emissions of existing plants would cut the net power output by 40% [28]. There are also some doubts about the technical potential for storage, given that adverse environmental consequences are possible. Because of possible leakage, the storage may prove only temporary [27].
Recently, interest in geo-engineering has been revived, because progress in tackling climate change has been far too slow compared with the emission reductions needed for climate stability [29]. The key advantage of geo-engineering is that it could be technically implemented in a short time frame-years rather than decades. The favoured method is to introduce sulphate aerosols into the stratosphere to offset global warming. But recent modelling has shown that while rapid cooling would indeed result, any cessation of aerosol placement through technical failure or political opposition would cause unprecedented rates of temperature rise-up to 20 times the present-day rates. Adaptation to such rapid rates of climate change would place severe stresses on ecosystems [30]. Further, since geo-engineering does not address the second serious problem of continued CO2 emission-progressive acidification of the oceans-it carries its own risks. It would also seem impossible to implement politically, since any adverse climate effects anywhere, particularly decreased rainfall, could plausibly and often accurately be blamed on such climate modification.
Policy makers prefer these technical solutions for transport problems. They see them as having fewer political costs, because lifestyle changes are not required as they would be for shift to more environmentally friendly travel modes, or to lower travel levels. Furthermore, it generally frees policy-makers from responsibility for solutions, which can be left to the holders of the technology, the vehicle manufacturers. Vehicle manufacturers, who in 2006 spent over $US 55 billion on research and development to support sales worth around $US 1.5 trillion [31], also prefer technical solutions, which allow them to continue their operations in preference to low-mobility solutions. However, as we have shown, sole reliance on technical solutions is unlikely to help much in either overcoming oil depletion or reducing transport greenhouse gas emissions-particularly in view of the urgent need for rapid action on both problems. As the French futurist Godet observes ‘Although we overestimate change, we underestimate inertia’ [32].
An examination of the history of transport technology shows that although genuine breakthroughs do occasionally occur, they are not as common as thought [2]. Technical advances in transport are sometimes only temporary, for a variety of reasons. One advance from the early 1970s, super-sonic commercial air flight, has been indefinitely abandoned with the retirement of Concorde services. Other technologies have been withdrawn because of adverse consequences, unforeseen at the time of introduction. Examples are leaded petrol, introduced to improve fuel octane rating, and CFCs in air-conditioning equipment, including that in cars. The constraints which every new technology must overcome are becoming steadily more severe, as we approach more and more ‘tipping points’ in the natural environment [21]. In summary, our increasing knowledge about the natural world may well advance some transport technology innovations, but it may also preclude others.
2.2. Possible economic constraints
High-mobility vehicular transport is costly, both for the individual motorist or air traveller, and also for the providers of the transport infrastructure. Furthermore, new transport technologies and fuels – such as hydrogen fuel cell vehicles, or renewable energy for electric vehicles – promise to be more expensive than existing technologies. Thus, high-mobility transport projections in turn depend upon continued strong economic growth; our earlier research found a strong linear relationship between global transport levels and real Gross World Product (GWP) over the years 1950–2000 [2]. The EIA, for example, assumes an average global annual real growth out to 2030 of 3.6% for their low economic growth case, and 4.5% for their high growth scenario [13]. Similarly, Riahi et al. [33] project real GWP in 2050 (as measured by market exchange rates) as rising to 4.8–6.5 times the 1990 value.
Peak oil writers regard the coming downturn in oil supply as having profound global economic repercussions [34] and [35]. Thus Campbell [34] argues that as we enter what he terms the ‘Second Half of the Age of Oil’, ‘some basic reappraisal of economic thinking is called for, given the fundamental role of oil as a fuel for most economic activity.’ Similarly, Curtis [36] argues that the twin challenges of global climate change and oil depletion will act to undermine globalisation, in part because very high oil prices effectively raise the tariff on low-cost goods imported from distant countries.
Even the concept of continued economic growth as an aim is under attack, from within the economist ranks as well as from outsiders. First, it is increasingly recognised that on a finite planet, exponential growth cannot continue indefinitely, and the multiple environmental and resource problems the world faces suggest that its end cannot be safely postponed to the distant future [37]; indeed since present assessments of economic growth ignore the true costs of resource use and pervasive environmental deterioration, actual growth may already have ceased. Second, Gowdy [38] has pointed out that empirical research has shown that for whole societies, as well as individuals, consumption levels, as measured by incomes, correlate poorly with happiness, once a minimum level has been reached. Yet all the scenarios discussed above assume that continued global economic growth is both possible, and implicitly, desirable, even in high-income countries. (Gowdy also stresses that the environmental collapses-often from adverse climate changes-that triggered the declines of previous civilisations were only local, but today we are increasingly threatened by global environmental collapse.) In short, future economic growth could cease to be humanly important, or it could prove progressively more difficult to achieve, or simply illusory-an accounting fiction.
We conclude that continuation of high-mobility lifestyles in the OECD, and even their spread to the rest of the world, is a possible future, but not very probable, for two main reasons. First, even if the needed technical breakthroughs do occur, they are most unlikely to make much impact in the limited time available. Second, because of the need to change from the present oil-derived transport fuels to overcome environmental and resource constraints, unit vehicular transport costs are likely to continue to rise, requiring that an ever-increasing share of the GWP be spent on transport. Since technology is unlikely to save high-mobility transport, we urgently need to examine low-mobility alternatives.
3. An ethical transport system?
In reaction to the value-free pretense of much technological forecasting, many prominent futurists stress the importance of ethics in thinking about the future [10], [11] and [39]. Unless the outcome is totally determined-the time for viewing of a lunar eclipse, for example-we cannot avoid making choices, whether we explicitly acknowledge them or not. To select or advocate a particular transport future is to make an ethical decision. Here we examine for the existing global transport system the human costs of traffic casualties, and the high environmental, social and political costs of both oil and its presently favoured alternative, biomass liquid fuels.
Globally, annual road traffic fatalities were estimated to already number around 1.2 million at the end of the 20th century, with a further 50 million persons with injuries of varying severity [40]. Nearly all global transport fatalities are from road transport: commercial jet air transport deaths, for example, in recent years have averaged only about 54 annually, although light plane deaths are much higher [41]. Traffic fatality levels per vehicle are inversely related to vehicle ownership, so-paradoxically most of these casualties are in low car ownership countries [25] and [40]. Indeed, Africa, with very low average car ownership, has the highest regional fatality rate per 10,000 people [25]. The reason is that low car ownership is inevitably associated with a high proportion of vulnerable road users – pedestrians, cyclists and motor cyclists – who account for most of the fatalities, and have much higher fatality rates per km travelled [40].
Casualties are projected to rise if the world proceeds further down the high-mobility path, because in very low car ownership countries (0–10 cars per 1000 persons), a doubling (say) of road vehicles – and thus vehicle occupants – only marginally reduces the number of vulnerable road users. A recent World Bank-funded study of the relationship between traffic fatalities and economic growth forecasts that global traffic fatalities will rise about 66% over the first two decades of this century, with a projected 30% decrease in wealthy countries more than offset by an 83% increase in poorer countries [42]. Even though the absolute number of fatalities is already falling in most OECD countries, the sharp rise seen in many poorer countries is anticipated to continue until national GDP/capita reaches $8600 ($US, 1985 values) [42]. Not only fatalities but serious injury can have catastrophic effects on low-income households, since it can involve both long-term loss of income and high medical expenses [40].
Many writers have pointed out the relationship between our desire for ever-rising volumes of oil and the civil unrest and even wars that it brings about (e.g. [43] and [44]), and the tensions in the oil-rich Middle-East are well-known. Nigeria can serve as a case study for the environmental, social and political problems that major production and exports of oil incur in newly industrialising but resource-rich countries. In the Niger Delta, an estimated 1000 people are killed each year in petroleum-related violence [43]. In addition, extraction of oil has produced a variety of health and environmental problems [45]. Numerous oil spills and gas flaring produce air, water and soil pollution, which in turn lead to serious problems such as respiratory illnesses, fish that are unsafe to eat, and loss of livelihoods for many residents of the densely populated Delta region. Recent oil prices may seem high for consumers in oil importing countries, but for many in the exporting countries, the human costs of oil are even higher.
Advocates of biofuels see them as both greatly cutting transport's greenhouse gas emissions as well as lessening our dependence on oil. Recently, doubts have been expressed about the ability of such fuels to address these problems without creating a new set of serious problems. At present almost all biofuel liquids are produced from food crops-grain, sugar and edible oils. Already the price of these crops is rising, since growers can now sell in two markets, energy and food [46]. Even non-food crops such as grasses and trees-if the technical/economic problems of the conversion of cellulose into liquid fuels can ever be overcome-often have their own serious environmental costs [47]. Apart from the limited production possible from biomass wastes, bioenergy plantations will still compete for food crops for fertile, rain-fed land, and may not even help mitigate climate change [48].
Extraordinary efforts are warranted for some projects—in particular, for avoiding global climate change, where urgent and timely action seems necessary to avoid irreversible loss of polar icecaps and other damaging changes. We have shown above that similar extraordinary efforts would be needed to allow a high-mobility future based largely on car and air travel to continue. But from the evidence presented here, it can be argued that the ethical costs of continuing – let alone expanding – our present transport system are simply too high.
4. A socially and ecological sustainable transport future
We have argued that the often-proposed technical fixes are not plausible—technology alone can only marginally cut transport-related greenhouse gas emissions or oil use in growth economies. And even if technological solutions were developed in time, continuation of the present transport system would bring unacceptable levels of human casualties and environmental damage. The shift to biofuels would also bring unwanted consequences—we cannot avoid ethical problems in transport simply by changing fuels. Since transport is nearly always a derived demand, we need to shift our focus from the provision of ever-expanding vehicular mobility, to the human needs that it is (presumably) meant to satisfy. We can then move to a transport future guided by ethical considerations, one less bound by the constraints of the existing system.
Regardless of any differences in culture, the world's people will have to live within increasingly more stringent environmental and resource constraints. So our minimum requirement for a desirable future would be a socially and ecologically sustainable world. This in turn would need to be based on a more egalitarian society, in which disparities both within and between nations were greatly reduced. Research should focus on the basic needs all people have for food, housing, access, sociality, health and sanitation, and devise new ways of meeting these demands with lowest human and environmental costs [49]. Exactly how these basic needs are met will vary from country to country. The recent IPCC Impacts Report [18] stresses that the burden of climate change (at least in the medium-term) will be disproportionately borne by low-latitude regions-precisely the regions least responsible for the cumulative CO2 emissions causing climate change. Ethical considerations would suggest that some rudimentary global welfare system needs to be put in place [50] to avert possible catastrophe in many countries from the synergistic effects of their existing ongoing problems and adverse climate change.
We will illustrate the potential for large energy and emission reductions from a human needs approach by considering what form future passenger travel might take in our own city, Melbourne, Australia. We focus on our own city, not only because we are familiar with its existing transport system, but also because of the risk of culture-bound generalisations [39]. In Melbourne, a city of 3.8 million, about 90% of passenger travel is presently by car, a pattern which has persisted for several decades. Yet in 1947, the year of the first post-war census, 80% of urban passenger travel was by public transport, mainly electric trams and trains. The change to 80% of travel by car took only 15 years. Overall surface vehicular travel for each of Melbourne's 1.2 million residents in 1947 was 3600 passenger-km, about one quarter of today's level. Although the focus for most vehicular travel then was the city's inner area, many suburban trips were local, and made on foot or bicycle [51].
Today, travel patterns are very different. Most travel is now for discretionary trips-shopping and entertainment, for example. The central area is no longer the focus of most vehicular travel; not only residences, but shopping centres and services of all kinds have suburbanised. Workplaces and workers are now more evenly balanced over the urban area. Personal travel levels could thus be much reduced compared with 1947, given that most vehicular travel undertaken was then essential because of workplace-residence separation. Instead, as we have seen, vehicular passenger-km/capita has risen almost fourfold. Some of this rise can be attributed to higher incomes. But much results from the higher door-to-door speeds of car travel compared with public transport (particularly for non-central destinations), the psychological benefits of car ownership and operation, and the rise of a new travel category, car chauffering trips, which form a growing share of today's travel [17] and [51]. These latter reasons for travel growth would disappear if car travel itself became marginal.
A new system based on a socially and ecologically sustainable world-view would see a reversion back to non-motorised (or active) transport and public transport. The new system would entail some replacement of vehicular transport energy by human effort-a partial reversal of the trend established by the Industrial Revolution. (This is not to say that our preferred solution could not benefit from technological advances, but does not rely on them. After all, electric public transport, buses, and cycles have all been in use for over a century, and walking is as old as humanity).
Some present benefits of private travel would be lost, such as privacy and the psychological benefits of driving, but the change would bring its own benefits. Not only would fewer vehicle traffic casualties result, but if allowable speeds for remaining road vehicles were greatly reduced, so would injury severity in the remaining collisions [25]. Active travel modes would now be safer and less stressful, and their more widespread use would enhance both human health and fitness levels [25]. The changes would also allow very large cuts in transport energy use and GHG emissions, given the much higher energy efficiency of alternative modes [17], a reduction in air and noise pollution, and in community severance from heavily trafficked arterial roads. Urban land presently used for car-parking, and some road space, could be freed up for other uses. The new system would be far more equitable, since it would not only be cheaper than a car-based system, but also would not limit access for those without a driving licence, as is presently the case.
It is not enough to describe the new system and give its advantages; we also need to explain how such a shift to sustainable transport can be realised. Transport oil consumption and emissions can in principle be reduced to any level desired by applying sufficiently high road use taxes or fuel prices. Given continued depletion of both global and Australian oil reserves, further externally imposed price rises for fuel are likely, leading to further reductions in petrol use and associated emissions. But market-based approaches alone for very large cuts in emissions are inequitable, given the greater travel needs, lower access to public transport, and lower average incomes of outer suburban Melbourne residents compared with those closer in [52]. A more equitable approach could include government policies such as much lower maximum road speeds, traffic-free precincts and greater parking restrictions in the inner areas, an end to further arterial road building, provision of extra public transport services, particularly in the outer suburbs and incentives for alternative travel modes. There is a local precedent for non-market solutions: in response to very low volumes in Melbourne's reservoirs, the state government has imposed restrictions on water use, rather than resorting to much higher costs for water.
The travel changes also need be implemented very quickly, as time is important if transport's oil and climate change challenges are to be effectively addressed. Impending oil shortages and the resulting fuel cost increases could act as a catalyst for change, and make its acceptance more likely. Further, building on the federal government's recent ratification of the Kyoto protocol, the just-released Garnaut interim report, commissioned by the state governments, calls for a 90% reduction in Australian emissions by 2050 [53]. Indeed, there are already signs that a transport change is underway in Melbourne. Public transport patronage is now growing rapidly; average weekday trips rose 5% in 2005–2006 and 8% in 2006–2007 [54]. And nationally, consumption of fuels for cars and light commercial vehicles has fallen since 2004 [55], despite strong economic growth and low unemployment.
Planning a transport system for an ecologically sustainable future requires some knowledge of future travel patterns. In Melbourne, as in other Australian cities, historical experience suggests that different dominant transport modes entail not only very different levels of personal travel, but also different travel patterns. In this sense, an active mode/public transport system would not merely replace existing travel by these new modes, any more than the car just replaced previous travel modes; dominant travel modes produce urban travel patterns, rather than merely enabling them to be undertaken. Hence, during the transition to a new system, it will be important for the public transport system to be able to respond rapidly to changes in both loadings and preferred routes. In the short term, higher passenger loadings could be accomodated on any existing under-utilised public transport services, then on additional services using existing fleets. Especially in the transition, buses will play a prominent role, because of the ease of developing new routes using the extensive existing road network. Expansion of the bus fleet will be necessary. Additions to Melbourne's already extensive fixed-rail train and tram routes, if needed, would of course take much longer to implement.
Much of the creativity and change needed for large travel reductions would come from individual households modifying their daily travel patterns in unique ways to adjust optimally to the new constraints. However, reducing travel is different from reducing domestic energy or water use, where households do not need to wait for general change to lower their own consumption. For transport, reductions depend much more on simultaneous changes by all households. If all now shop locally, local shopping centres become more viable, and a more attractive destination than more distant ones. Similar considerations hold for local entertainment, recreational and educational centres. Indeed, all activities, including work, would need to be far more locally based than is presently the case. Because of this need for city-wide changes, supporting government policies will be essential.
Looking beyond urban transport, air travel, non-existent in 1947, now averages about two annual trips for each Australian [5]. A new low-mobility transport system would also need drastic reductions in air travel; reductions could come about through greater use of more local destinations for holidays in place of international ones, for example. A trip overseas might have to become a once-in-a-lifetime experience, not an annual event.
What then are the benefits of a more general adoption of this approach to future global transport? In countries with income levels similar to Australia's it could be argued that the benefits would be similar. For poorer, low-mobility countries the benefits are potentially greater. A large reduction in greenhouse gases – transport-related or otherwise – by presently wealthy countries would allow greater energy consumption in very low-income countries. Perhaps an even greater benefit would be to signal to the rest of the world that continuation of the present high-mobility transport trajectory is an illusory future, one that could either only be maintained by a small proportion of the earth's population, or if generally adopted, for a short time. In the absence of significant technical breakthroughs and limited renewable energy, a sustainable future implies a roughly fixed quota of both energy and emissions, including those for transport. Clearly, in a more equitable world, continued global population growth would result in steadily diminishing quotas of both for all.
5. Conclusions
Most recent analyses of global transport envisage vehicular passenger travel continuing its growth of recent decades. Indeed, the literature on transport futures is dominated by two assumptions: first, that global vehicular travel demand can and should increase indefinitely (like economic growth, upon which it depends), and second, that the increasingly acknowledged global oil depletion and adverse climate change challenges to travel growth are capable of technological solutions. These solutions include greatly improved vehicular fuel efficiency, alternative fuels and even propulsion systems, and carbon capture and storage. We have questioned whether these optimistic solutions can be developed and widely deployed in the limited time frames available. The lack of progress in both vehicular fuel efficiency and penetration of low-carbon fuels are examples of the long time frames needed for fundamental changes in energy and transport technology and infrastructure.
Not only are ever-rising vehicular mobility levels unlikely to occur, but the human costs of continuing this approach are also too great. The world's road-based transport systems presently kill over 1.2 million people each year, mainly in low-income countries. This death toll is projected to rise if motorisation continues its sharp growth in presently low car-ownership countries. In the oil-exporting countries themselves, oil production often produces serious environmental problems, social strife, and even wars. Current interest in expanding bio-fuels could also have disastrous outcomes for the world's poor, if cropland is increasingly diverted away from food production.
Future passenger transport most probably cannot, and should not, continue on the path forecast and usually advocated by most transport projection studies. Ever-rising mobility is more an imperative for transport-related corporations than a basic human need. A new approach to transport is needed, one that both better fits in with the need for a socially and ecologically sustainable world, and that recognises travel as a mainly derived demand. For our own city of Melbourne, an analysis of the past 50 years of travel suggests that a reversion back to active modes and public transport would enable major progress toward such a future. General adoption of similar policies by other high-mobility societies would both signal the end of high-mobility lifestyles to the rest of the world and free up resources for the poorest countries.
Acknowledgements
Patrick Moriarty would like to acknowledge the financial support of the Australasian Centre for the Governance and Management of Urban Transport (GAMUT) in the preparation of this paper.
References
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