Accepted Manuscript

Greening passenger transport: A review

Patrick Moriarty, Damon Honnery

PII: S0959-6526(13)00209-6

DOI: 10.1016/j.jclepro.2013.04.008

Reference: JCLP 3397

To appear in: Journal of Cleaner Production

Received Date: 21 November 2012

Revised Date: 1 April 2013

Accepted Date: 4 April 2013

Please cite this article as: Moriarty P, Honnery D, Greening passenger transport: A review, Journal ofCleaner Production (2013), doi: 10.1016/j.jclepro.2013.04.008.

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Greening passenger transport: A review

Patrick Moriartya1 and Damon Honneryb

a Department of Design, Monash University, P.O. Box 197, Caulfield East 3145, Vic., Australia

b Department of Mechanical Engineering, P.O. Box 31, Monash University, 3800 Vic., Australia

Abstract Passenger and freight transport are responsible for nearly a quarter of global primary energy use and energy related greenhouse gas (GHG) emissions. Given the rapid rise in transport in industrializing countries, particularly China and India, this fraction is expected to increase in the coming decades. In the context of the need to reduce transport energy and GHG emissions, this paper addresses the following question: Should most of our efforts to reduce transport energy use and GHG emissions concentrate on reducing emissions (or energy) per unit of transport task (e.g. kg CO2-equivalent per passenger-km), or should we rather focus on reducing the passenger transport task itself? In addressing this question we limit our examination to surface passenger transport, since this makes up a signifciant proportion of all transport GHG emissions. We show by consideration of the available literature that it is most unlikely that technical solutions alone can deliver anywhere near the reductions needed. We then examine proposed non-technical solutions and conclude that major transport policy changes that reduce passenger travel levels themselves will be most effective in producing timely and deep transport emission cuts in existing economies. We end by discussing the prospect for these approaches in the transport sector and the broader economic consequences. Keywords: de-growth, greenhouse gas reductions, non-technical solutions, technical solutions, transport policy, urban transport

1 Corresponding author. Tel: +61 (0)3 9903 2584; fax : +61 (0)3 9903 2076. email: patrick.moriarty@monash.edu

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1. Introduction Global vehicular transport—both passenger and freight—in 2009 accounted for 27.3% of total final consumption of energy. The total transport-related figure would be even higher, since additional energy is required to manufacture and maintain the vehicles, construct the

roads and bridges, and dismantle the vehicles at end‐of‐life. In a business-as-usual world, this

proportion seems set to rise, given that in the Organization for Economic Cooperation and Development (OECD) countries, the corresponding figure was 32.7% (International Energy Agency (IEA) 2012). Global final transport energy (petrol, diesel, traction electricity etc.) has risen from 39.2 EJ (EJ = exajoule = 1018J) in 1970 to 96.3 EJ in 2010, an average annual growth rate of 2.3%. In primary energy terms, transport accounted for around 23% of the world total, with a similar share of CO2 emissions from energy use. Passenger transport accounts for about 60% of transport’s total energy use and greenhouse gas (GHG) emissions (Kahn Ribeiro et al. 2007).

Schafer and Victor (2000) in their analysis of global passenger transport, foresaw both non-motorized modes and public transport accounting for ever-decreasing shares. Their argument was based on the existence of fixed travel time budgets and continually rising incomes per capita. Although per capita total passenger-km was assumed to increase at least out to 2050, the end of the forecast period, travel time budgets necessitated that slower modes were progressively abandoned. For North America, an already-heavily motorized region, per capita car travel was predicted to peak around 2010. Per capita travel overall there would rise to over 50,000 passenger-km by 2050, with high speed modes (mainly air), supplanting car travel. Globally, however, car travel would continue to rise, roughly doubling its 2010 value by 2050.

Several studies have also projected private vehicle numbers out to 2035 or later. The Organization of the Petroleum Exporting Countries (OPEC 2012) expects passenger vehicles to rise from nearly 870 million in 2009 to 1.76 billion in 2035. The OPEC report saw most cars in 2035 owned outside the OECD countries, but even so, car ownership in OECD countries would still be four times higher than in industrializing countries. Meyer et al. (2012) modeled regional and global car ownership out to 2100. Their global results gave a range 1.4 to 2.0 billion cars for 2035, and 1.7 to 2.8 billion for 2050. The forecasts of the World Energy Council (2011) were somewhat smaller: 1.3-1.5 billion cars by 2035, 1.8-2.1 billion by 2050.

Concerns about global oil depletion and the desire for energy security have prompted the search for alternatives to oil as a transport fuel. Unconventional oil reserves are large, but expensive to develop. The Energy Information Administration (EIA) (2011) forecast production of unconventional oil in Canada to rise from 1.7 million barrels per day (mbd) in 2009 to only 6.5 mbd by 2035 in the best case (high world oil prices). The shift from oil has been very slow; petroleum products accounted for 94.4% of final demand for transport fuels in 1970, and 93.5% in 2010 (IEA 2012). Future oil availability is not the only factor driving the search for alternative fuels and propulsion systems. Regional, particularly urban, air pollution from transport is also of concern, especially in countries that are rapidly motorizing. It is argued that oxygenated fuels such as gasohol are already lowering air pollution levels. Further, urban transport air pollution could be eliminated if the entire road fleet consisted of battery electric or hydrogen fuel cell vehicles.

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Global climate change is also an important driver for alternatives to petroleum-based transport fuels, particularly for the European Union (EU). It may soon become a global force for change, for the following reason. Although global average surface temperatures have risen by 0.7-0.8 °C since preindustrial times, this has not really mobilized people in OECD countries. As Hansen et al. (2012) pointed out: ‘The greatest barrier to public recognition of human-made climate change is probably the natural variability of local climate. How can a person discern long-term climate change, given the notorious variability of local weather and climate from day to day and year to year?’ What is likely to trigger decisive action for mitigation is a rapid change in the frequency and severity of events resulting from extreme weather conditions, such as floods, droughts, heat waves and wildfires. These changes already appear to be happening, and at a rate even faster than predicted by the IPCC reports (Battersby 2012). These extremes are occurring over a progressively rising share of the Earth’s surface (Hansen et al. 2012), and so are already being personally experienced by an ever-increasing proportion of the global population.

In general, the published research sees technical solutions to these transport problems (and to the problems of energy use in other sectors as well) as far more important than solutions that advocate lifestyle changes to reduce the use of energy-using devices. Accordingly, this paper addresses the following vital question: Should most efforts to reduce passenger transport energy use and GHG emissions concentrate on reducing emissions (or energy) per unit of transport task (kg CO2-equivalent (CO2-e) per passenger-km), or should policy-makers focus on reducing vehicular passenger-km itself?

Section 2 briefly outlines the approach that guided the selection of reviewed research. Section 3 examines technical solutions for transport, and concludes that they cannot deliver the greenhouse gas reductions needed, although their potential is greater for local air pollution. Section 4 discusses possible non-technical approaches. While very large increases in urban density would reduce travel, they would not only take many decades to implement, but could conflict with other urban sustainability aims. Transport policy changes, for example, large reductions in vehicle speed limits, have far greater potential, as well as being much cheaper and far faster to implement.

2. Approach taken

This review examines whether technical solutions are sufficient to ‘green’ surface passenger transport. Surface passenger transport is selected because it the major contributor to transport GHG emissions; the review does not cover freight transport, nor does it consider air travel. The word ‘technology’ has both an extended and a restricted meaning. Technology is generally defined as the science of mechanical and industrial arts, and it is in this restricted sense that technology, and by extension the word ‘technical’, are used in this review when distinguishing technical and non-technical solutions.

Section 3 reviews the ‘Technical solutions for transport’, both in and out of the OECD, since alternative fuels such as ethanol and natural gas have been adopted by a wide range of countries, and given the globalization of the vehicle industry, car designs do not vary much. This section does not consider the energy embodied in the construction of vehicles themselves or of the road infrastructure; it only looks at papers concerned with the full fuel cycle for vehicles. The reason for this omission, apart from the lack of good recent data for most countries, is that road infrastructure energy costs are largely sunk costs, and will not necessarily decrease much if vehicles are made more efficient or even smaller. Also, according to Usón et al. (2011), at least in the EU, vehicle manufacturing only uses 15-20% of the energy needed for vehicle operation.

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Section 4 reviews ‘Non-technical solutions for transport’. It uses as primary references the data compiled by Newman and Kenworthy (1989, 1999) and Kenworthy and Inbakaran (2011) on a comprehensive set of various transport and land use parameters for a large sample of the world’s major cities. The earlier works presented data covering 1960 to 1980, the later work extended the range to 1990, and for 13 cities, to 2006. The full coverage for 1960 to 1990 is only for OECD cities, with the exception of Hong Kong and Singapore. This review likewise mainly restricts its coverage to cities of the OECD, for two reasons. First, reliable time series data on transport and land use parameters are usually not available for non-OECD countries. Second, not only are incomes often lower in industrializing compared with OECD countries, but urban densities, particularly in Asian cities, are usually very high, and further increases may not even be desirable.

Much of the research on the relationship between land use and transport is only concerned with assessing the effect of land use changes on a small area of the city. As Cao et al. (2009) and other researchers have observed, the results can be difficult to interpret because residents often choose to live in more densely built-up areas of the city. Because of this difficulty, and because cities function as a system (Section 4.1), studies of transport and land use in individual areas of a city have been excluded.

In Section 5, we explore the the broader consequences non-technical solutions to provide the needed cuts in transport GHG emissions and extend the discussion by considering the potential of non-transport specific proposals such as degrowth. In doing so we draw in particular on the literature featured in recent issues of the Journal of Cleaner Production. We conclude this section by a discussion on the likelihood of success of these approaches.

3. Technical solutions for transport This section examines the technical solutions that have been proposed for greening passenger transport. Strong forces are at work promoting technical solutions to the challenges thrown up by the expanding global transport task documented in Schafer and Victor (2000). Vehicle manufacturers want to sell automobiles, if possible at an increasing annual rate. They are not directly motivated by solutions to road transport’s environmental problems that involve car travel reductions, which would cut total expenditure on vehicles. Similar considerations apply to fuel vendors, road construction firms and providers of services to transport. While they may be genuinely concerned about transport emissions and are working to reduce them, they they are still motivated to sell more vehicles and fuel. (Although individual vendors will be content to merely gain increased market share or rising profits, the overall result will be pressures to expand vehicle use.)

Responding to increasingly stringent exhaust emission regulations, technical solutions implemented by vehicle manufacturers have largely been successful in reducing air pollution in the highly-motorized cities of the OECD. Lead-free petrol and low-sulfur fuels have helped cut urban emissions of lead, SOx and particulates. Three-way catalytic converters have been mainly responsible for lowering emissions of CO, hydrocarbons and NOx. Also, along with improved education and enforcement, technology in the form of seat belts and airbags has sharply cut traffic fatalities—at least in OECD countries.

Researchers over recent decades have therefore come up with a number of technical fixes for solving the air pollution and traffic safety impacts of vehicular transport. For the two main challenges to the sustainability of existing transport, GHG emissions and global oil depletion, proposed solutions by researchers include the use of alternative fuels and vehicular power systems, and large improvements in vehicular energy efficiency. Andress et al. (2012) give a comprehensive overview of ‘cost, technical, infrastructure, and market barriers’ for these

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various technologies in a US context. Given the needs of the transport industry for continued growth in passenger transport, technical improvements in the form of lower fuel use or emissions per passenger-km will always be in a race against increases in total passenger-km. Since per capita levels of transport are on average far lower in the industrializing countries than in the OECD, global transport growth is expected to be rapid, as discussed in the Introduction.

Another difficulty with reliance on technical solutions is that there is today no clear future direction for new technology for road passenger vehicles. In recent decades battery electric vehicles (EVs), plug-in hybrid EVs, hydrogen fueled vehicles (both fuel cell and internal combustion engine), and conventional or hybrid vehicles powered by biofuels have all been strongly promoted by both industry and academic researchers as the future for transport. So have conventionally powered- and fueled-vehicles with greatly improved efficiency. Although they might all find a place in the future, it is still true that the large production volumes needed for cost reductions will be difficult to achieve if spread among a number of vehicle types. Geels (2012) has even used the term ‘hype-disappointment cycle’ to describe the rise and fall of enthusiam for these various newly-introduced (or reintroduced) technologies. Battery EVs have already had several such cycles over the history of the car.

3.1. Energy efficiency improvements When we consider improving the system-wide energy efficiency of transport vehicles, we need to consider how to reduce each of its three components:

1. The energy output from the propulsion system needed per unit of transport output (e.g.vehicle-km)

2. The energy in the fuel tank needed per unit energy output from the propulsion system

3. The input energy (for exploration, production, refining and delivery) needed per unit of energy in the fuel tank.

For land surface vehicles, the first point refers to the ‘road load’—the sum of air, rolling and inertial resistance—which can be reduced by decreasing the tare weight of the vehicle, and by cutting air and rolling friction. The second point refers to the efficiency of the propulsive system itself, including the power unit and the drive train. Much research has focused on these two areas, with fuel efficiency measured as passenger-km per MJ of tank fuel, although mandated targets are normally expressed as grams of CO2 per vehicle-km (gCO2/v-km). For land surface vehicles it is generally agreed that electric drive will give the highest efficiency, partly because it readily allows regenerative braking.

The theoretical scope for energy efficiency improvements from the first two components is large. Cullen et al. (2011) considered that passenger vehicle energy efficiency could be vastly improved, and governments are relying on these potential improvements to meet future targets.

In an attempt to mirror the success in meeting the technical challenges posed by more stringent exhaust emission regulations, many governments (e.g. those of the EU countries) now set targets for new vehicle tailpipe emissions in gCO2/v-km. Vehicle manufacturers are generally required to meet these standards across their sales within the relevant jurisdiction. Although vehicle sales are global, large variations exist across governments in both current and future targets. The EU, for example, requires manufactures to meet 130 gCO2/v-km by 2015, falling to 95 by 2020, while in the US, the target fleet-average is equivalent to 172

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gCO2/v-km for vehicles manufactured between 2012-2016 (International Council on Clean Transportation (ICCT) 2011).

The technical challenge in meeting targets should not be underestimated; many manufactures in the EU have failed to meet past targets (An et al. 2007), although these targets were then only voluntary. Actual emissions from real-world driving have also been found to be worse than those measured during the test mandated to measure emissions. A study undertaken in Germany by the ICCT for example found the gap between actual and test emissions increasing from 8% in 2001 to 21% in 2010 (Mock et al. 2012). Further, rates of improvement in emissions are failing to meet those needed to achieve the global target of 94 gCO2/v-km for 2030 developed under the Global Fuel Economy Initiative (GFEI); in 2008, the global average was estimated to be 179 gCO2/v-km (GFEI 2011). In a comprehensive study by Dray et al. (2012) on the maximum possible emission reductions from changes to transport technology alone for the European Union, it was found that efficiency of new passenger vehicles and light trucks might be improved by around 1% per annum, at least up to 2050, well below the rate needed to achieve the GFEI 2030 target. Improvement in fleet average fuel economy has been gained, for example, through the increased use of smaller vehicles powered by relatively efficient turbocharged engines (GFEI 2011), but such gains can be expected to stall once market saturation is reached. Also, vehicle manufacturers, following consumer preferences, will often promote vehicle performance at the expense of fuel economy. Future improvement will likely require use of alternative fuels and power systems; we discuss the prospects for these in Section 3.2.

Importantly, emission targets only apply to new vehicles, so emissions for the existing fleet as a whole can be expected to be much higher. In the US for example, new vehicles averaged 226 gCO2/v-km (GFEI 2011), but the passenger vehicle fleet average was estimated to be 276 gCO2/v-km (Schipper et al. 2010). Differences depend on factors such as historical sales trends, scrappage rates and vehicle usage. To give some perspective to the technical challenge facing manufacturers, the EU target for 2050 is to reduce all GHG emissions by 80-95% of their 1990 values (Dray et al. 2012). An extreme scenario might require passenger transport to make similar reductions.

The third component highlights the increasingly important distinction between gross energy (the total energy output) and net energy, often ignored in energy efficiency discussions. The net energy from an oilfield, for example, is the difference between the energy content of the extracted oil over the field’s life and the input energy needed to find and develop the field, extract all the oil and deliver it to a refinery. As long as delivered or net energy is a high fraction of gross output energy, the distinction between the two is not important. However, the net energy delivered as a fraction of gross energy for fossil fuels is falling, as the low-cost fields usually developed first also have lower input energy costs per unit of output (Cleveland 2005, Dale et al. 2011).

This divergence will increase as output of non-conventional fossil fuels, particularly non-conventional oil, forms a rising share of total output. Energy analyses done on Canadian oil sands show its much higher energy inputs per liter of fuel delivered to a vehicle’s tank, compared with conventional oil (Strahan 2009). If oil consumption grows as assumed in EIA and IEA business-as-usual assumptions, and conventional oil production follows the production profile given in Campbell (2012), the share of non-conventional oil must rise rapidly. It is even possible that any future gains in vehicle energy efficiency (components one and two) will be entirely offset by rising costs for delivering net energy.

3.2. Alternative fuels and power systems

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Alternatives to petroleum-based fuels include other fossil hydrocarbons (natural gas, liquefied petroleum gas, coal-to-liquids), electricity and bio-liquids. Alternative hydrocarbon-based fuels are, at best, of marginal use for GHG reductions (Moriarty and Honnery 2008). NGVA europe (2012) estimated that natural gas (NG) vehicles numbered about 14.5 million globally at the end of 2011, up from only 4.0 million at the end of 2004. Nearly all (13.8 million) were passenger cars, with most of the total in Asia or Latin America. The natural gas industry is urging their increased use in the US (Andress et al. 2012), given recent shale gas developments. Alvarez et al. (2012), argue for the US, however, that leakage from natural gas pipelines must be substantially reduced before any GHG reduction benefits occur. For shale gas in the US, measurement of methane concentrations in the air above developed fields suggests that fugitive emissions are also high. Methane is around 25 times more efficient at trapping outgoing thermal radiation than CO2 (Davis et al. 2012, Tollefson 2012).

Use of bio-liquids to fuel transport vehicles does go some way toward solving the oil depletion problem, but will only reduce GHG emissions if their kg CO2-e/MJ over the full fuel life cycle is less than that for petroleum-based fuels. Ethanol from corn (and other grains) or cane sugar, and biodiesel from oil seeds account for nearly all bio-liquids today. Researchers disagree as to whether these sources have lower GHG emissions than petroleum-based fuels. In Brazil, ethanol from sugar cane has less than 1/3 the emissions (in kg CO2-e/MJ) of petrol, but emissions of other non-GHG air pollutants are far higher (Tsao et al. 2012). For the US, researchers disagree as to whether or not corn ethanol produces net energy, but all agree that the energy surplus and GHG emission benefits are, at best, minor (Gomiero et al. 2010). This controversy may become less relevant in the future, as it is probable that food-based bioenergy sources cannot be expanded much further (Giampietro and Mayumi 2009, Gomiero et al. 2010). If biofuels are to form more than a few per cent of total transport fuels, cellulosic-based liquid fuels are needed. Since no cellulosic ethanol is commercially produced, their emission reduction potential and unit costs are uncertain. Although emissions from genuine waste biomass may be small, major production will necessitate energy plantations.

It will then be important to consider system-wide effects, as is already the case for food-based biomass inputs. Global terrestrial Net Primary Production (NPP) has an annual energy value of about 1900 EJ. Humans today appropriate up to 40 % of NPP, mostly for the world’s large and still rising needs for food, fibre, forestry products, and forage for farm animals. Such a high use of NPP by humans is already contributing to extinction rates of other species at 100-1000 times the background rate (Rockström et al. 2009). Adding energy production to our already high use of NPP could accelerate this species loss. Further, use of land for biofuel plantations is likely to accelerate land conversion for agriculture in the tropics, where most of the world’s land conversion already occurs. Carbon loss from land cleared in the tropics per unit of food output is three times that for temperate lands (West et al. 2010). When all GHGs, including N2O emissions, and climate change effects are accounted for, even cellulosic liquid fuels could well show little climate change benefit over petroleum fuels (Felix and Tilley 2009).

Using electricity for transport similarly reduces oil consumption, but only reduces GHGs if sourced largely from non-fossil fuels (RE and nuclear energy). In 2011 such fuels provided 31.8% of the energy inputs for global electricity generation, down from 37.5% in 1995 (BP 2012). The overall decline results from the falling share of nuclear power, which could prove difficult to reverse after the accident at Fukushima in 2011, even though Japan now plans to restart its nuclear plants. What are the prospects for non-fossil electricity over the years to 2035 or 2050? The EIA (2012) in their Base Case expect the combined share of RE and nuclear generation capacity to rise slowly from 32.9% in 2009 to 41. 5% in 2035. (The share

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of non-fossil fuels in electricity generation today is higher than for total primary energy, where the 2009 value was 19.1% (IEA 2012)).

Although new RE sources can and usually do show rapid initial growth, as is presently the case for solar energy (BP 2012), experience shows that as output rises, exponential growth is replaced by linear growth or even stagnant output. Roughly linear growth has long been the case for hydropower, and now may be the case for wind power (BP 2012). The Global Wind Energy Council (GWEC) (2012) appears to recognize this trend, projecting only linear growth in installed wind turbine capacity out to 2016. The decline in output capacity growth can occur for a number of reasons: suitable high wind speed sites may become limited; citizen opposition may intensify because of environmental costs or loss of amenity; larger output may mean that subsidies may become too expensive for governments to maintain, particularly in these economically difficult times. Overall, rapid increases in the market share of non-fossil electricity are not likely, given their continuing decline in share, and the difficulty of integrating large amounts of intermittent RE into electricity grids.

In summary, technical solutions to private transport’s GHG emissions are unlikely to be effective. The forecasts for global car numbers in 2035 given in the Introduction imply an average annual growth rate of nearly 3%. If both emissions and annual km traveled per car remain constant, CO2 emissions would grow at the same rate. Also, specific emission reductions from fuel efficiency gains would have rebound effects on total vehicle-km. Hence, just to keep car emissions at a constant level would need about a 3% reduction each year in gCO2/v-km, and perhaps double this level for the required absolute cuts. Such annual

improvements would be unprecedented (Millard‐Ball and Schipper 2011). But if, as argued in

Section 5, vehicle numbers stagnate globally, or even fall, annual sales will be low, the fleet will turn over very slowly, and vehicles requiring new propulsion systems may not even be introduced. Thus gCO2/v-km will again fall very slowly.

4. Non-technical solutions for greener transport Many of the non-technical solutions for greening transport focus on urban areas. In high-income countries (and even in middle-income Latin American countries) over 80% of the total population already live in urban areas (United Nations 2012). In Australia, where over 90% of the population is urban, 75% of both all travel and all fuel used by light vehicles occurs in either capital or provincial cities (Australian Bureau of Statistics (ABS) 2011). Transport in urban areas is therefore a vital part of total transport energy and emissions in high- and middle-income countries, so greening urban transport is the main emphasis of this section.

One obvious way to reduce transport, whether urban or non-urban, is to push transport costs to high levels, perhaps by a high carbon tax. Although oil prices will probably continue to rise if non-conventional oil sources such as oil sands or deep-water oil increase their share of global oil production, very high increases in transport costs as a policy measure would be inequitable in OECD countries with mass car ownership, because car vehicle-km per unit of income is often highest among low-income households. In Australian cities, reliance on car travel is highest in the outer suburbs of large cities. Residents of outer suburbs not only have greater travel needs than residents of inner or middle suburbs, but also inferior access to public transport, and lower per capita incomes (Moriarty 1998). Steep rises in car travel costs

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would thus heavily penalise them. (Similarly for the New Zealand city of Christchurch, Rendall et al. (2011) showed that, compared to a central city location, their outer suburban study area was less resilient to fuel price rises, since far fewer destinations could be accessed by active modes.) These same disadvantages also apply to non-urban populations. Nevertheless, it is possible that the rise in petroleum prices has been at least partly responsible for the documented recent fall in per capita car travel in the US and a number of other OECD countries (Bureau of Infrastructure, Transport and Regional Economics

(BITRE) 2012, Millard‐Ball and Schipper 2011). The US, with its low petrol taxes,

experienced percentage changes in petrol costs higher than in other OECD countries.

4.1. Land use changes

Fortunately, increasing the cost of motoring is not the only policy option available. Other non-technical options can be grouped into two general themes. The first involves various forms of urban land use change, especially residential density increases. The second group are transport policy measures (apart from increases in the monetary costs of motoring) that directly or indirectly influence car travel speeds and car access, such as lower speed limits and parking restrictions.

Many researchers (e.g. Boarnet et al. 2010, Karathodorou et al. 2010, Litman and Steele 2012, Newman and Kenworthy 1989, 1999) have regarded land use changes, particularly urban density increases, as an important means both for reducing overall vehicular urban travel, and for increasing public transport patronage, or use of active travel modes. Newman and Kenworthy (1999) found for a sample of 46 global cities that per capita passenger-km and transport fuel use, both for private transport only and for all vehicular passenger travel, had a roughly exponential relationship with urban density. (Fuel use for all urban transport, both passenger and freight combined, also varied strongly with urban density.) Differences in travel per capita between densely populated Asian cities and the less dense Australian or North American cities are large, as is also public transport’s share in total vehicular travel. One difficulty with such comparisons is that a number of these lower-mobility Asian cities also had much lower per capita incomes than typical OECD cities.

An even more serious problem for land use change relates to urban density measurement. Different countries define city boundaries differently. This is problematic because in large cities, resident travel per capita often tends to be higher as the resident’s distance from the city center rises. Large cities are usually structured with the Central Business District—and the Inner Area generally—supporting a number of activities important for all metropolitan residents, not just local residents. The city center may be the focus for major cultural, educational, sporting, entertainment, specialist employment and shopping activities. The data in Newman and Kenworthy (1999) show that the ratio of jobs to resident workers is on average more than twice as large for Inner compared with Outer Areas for their sampled cities. This difference helps explain the longer average commuting trips distances for Outer Area workers. Most of the difference would still remain even if Outer Area residential densities were similar to those of the inner area. The middle and outer areas of a city are not just an appendage to the inner city area. The excess of jobs to resident workers in the inner area (and the similar excess in shopping or entertainment expenditure) would not be possible without the middle/outer area workforce and their expenditure.

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If outer suburbs are excluded from the city definition, measured average travel per capita will be lower, and public transport’s share will be higher. Inconsistent definitions probably explain part of the lower per capita travel in European cities compared with those in Australia or North America. Even for a given city, published values in the literature can vary greatly. A comparison of Newman and Kenworthy (1999), Kennedy et al. (2009) and City Mayors (2012) shows estimates for urban density of a number of world cities that vary by a factor of up to five for a given city.

For cities with density measured on a consistent basis, such as Australian capital cities at each census, the travel reductions found with higher urban density cities may be small. The urban densities of Australia’s five cities of over one million population vary by a factor of two, but travel per capita by a few percent only (ABS 2006, BITRE 2012). If density change is to be a policy measure, it is also important to look at how actual density changes in a given city over time have affected passenger travel levels. Kenworthy and Inbakaran (2011) presented data for urban density and car passenger-km/capita for 13 OECD cities for the years 1996 and 2006. The unexpected result for five of these cities was that personal travel levels either rose as density rose, or fell as density fell. Urban density increases alone evidently cannot guarantee car travel decreases.

Large rises in urban density would be very difficult to achieve, for two reasons. First, even a doubling of urban density in the typical cities of Australia or the US could be expected to take many decades, given the longevity of urban infrastructure. A survey of non-residential buildings in North America (O’Connor 2004) showed that their expected lives were 52, 76, 77, 86 years for wood, steel, masonry and concrete buildings respectively. Residential buildings should have similar potential life expectancy. Thus any density increases would be strongly dependent on large urban population growth rates. Given the high existing level of urbanization in OECD countries, sustained high urban population growth rates seem unlikely. It may even be the case that in future a modest shift away from cities will occur, driven by the need for more agricultural labour.

Second, very high overall density increases could be expected to meet strong local opposition. It is true that local re-development at higher residential densities of under-utilized land (such as various docklands redevelopments, or derelict buildings in Denver’s lower downtown area) may attract popular support. Nevertheless, these developments do little to raise average urban residential density for the entire city, particularly in the face of the continued decline of household occupancy rates (see, e.g., ABS 2006, Statistics Bureau, 2013, United States Census Bureau, 2012).

Furthermore, urban sustainability entails much more than a sustainable transport system. Cities may well need to produce more food, especially fruit and vegetables, in urban gardens, and also be at least partly self-sufficient in water, with rain-water tanks in low or unreliable rainfall areas. Sustainability might also need more energy self-sufficiency in the form of roof-top solar energy systems and far more reliance on passive solar energy and natural lighting. High urban densities will make all these innovations much more difficult, as Steemers (2003) found for higher density living (apartment blocks rather than separate houses) in the U.K. On the other hand, higher densities are advantageous for reducing winter heat losses.

A further conflict with overall sustainability can arise if high urban densities reduce area for parks, especially in the inner areas of cities. Natural vegetation, especially trees, can exert a local cooling effect, which can improve the local thermal environment in hot climates. For Singapore, Yu and Hien (2006) found that the presence of large vegetated parks in this island city state decreased temperatures not only inside the two parks studied (12 ha and 36 ha in area) but also in adjacent built-up areas. Their modelled results showed a maximum 10% reduction in cooling load for buildings adjacent to the parks. Judicious planting of vegetation can thus reduce the local air-conditioning load in warmer climates.

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4.2. Transport policy changes Changes in urban density large enough to markedly reduce transport vehicle-km, and so transport energy and CO2 emissions, would, as shown in Section 4.1, be both unpopular and take many decades to implement. It would also be unnecessary, as we demonstrate in this section. We need to remember the purpose of passenger travel. Travel is largely a derived demand, involving the expenditure of both time and money in order to access out of home activities. Access to activities, not vehicular mobility, is crucial.

The low density cities of Australia and North America did not always have such high levels of passenger travel (Newman and Kenworthy 1989). During the public transport era of Australia’s largest cities, which lasted until around 1950, per capita vehicular travel levels were typically only about one-quarter of today’s levels. Vehicular trips were heavily oriented toward the central city area, where most jobs, entertainment, sporting and retail activities were concentrated. It is thus useful to consider a very simple urban model in which all activity requiring vehicular travel for access is concentrated in a small central area, and that the number of trips per person annually to and from this central area (for work, shopping, entertainment etc) is the same for all cities, regardless of size. Total vehicular travel per capita will then be N*d, where N is the annual number of trips to and from the center, and d is the average resident distance in km from the center. It follows that if cities are of roughly equal density, residents of larger cities will have greater travel per capita simply because on average they will live further from the center. This simple model was a fair approximation to Australian urban travel in 1947, toward the end of the public transport era (Moriarty and Honnery 2005).

In this model, there is zero excess travel. Excess travel for commuting, for example, is ‘calculated as the difference between the actual and minimum average commuting distances’ (Suzuki and Lee 2012). At the minimum average commuting distance, no possible swapping of either houses or workplaces by the resident workforce could reduce total vehicular work travel. Similarly, minimum shopping travel would occur when each resident travelled to the nearest shopping center of a given size. The concept can evidently only be loosely defined for non-commuting trips. Today, however, with the rise of the service economy, workplaces, retail centers and destinations of all kinds are far more uniformly distributed over the urban areas in OECD cities (ABS 2006, Newman and Kenworthy 1989,1999). This dispersion has two consequences. First travel levels could potentially be much lower because of reduced trip lengths (Moriarty and Honnery 2008). Instead, as noted, travel levels have risen greatly in OECD cities since 1950. The second is that such dispersion gives rise to the possibility of excess travel.

Several research papers have examined the size of this excess travel for the journey to work trip. For 1981, Moriarty and Beed (1988) found that the excess commuting fraction varied from 0.46 to 0.54 for the four large Australian cities studied. More recently, Suzuki and Lee (2012) found a 0.49-0.67 range for 26 US cities in 1990, but only a 0.18-0.41 range for 12 cities in Japan and South Korea in the year 2000. Particularly in US and Australian cities, total work trip passenger-km could be cut in half, even with the existing location of residences and workplaces, if enough workers switched either residences or jobs. Analysis of shopping patterns in Australia’s capital city, Canberra, suggested that much excess travel also occurs with shopping (Moriarty and Honnery 2005).

A possible reason why per capita travel has risen greatly, even though it could have potentially been reduced, is the convenience of car travel compared with other modes. (Rising incomes were also important, not least for enabling money for car purchase and travel.) Car

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travel convenience can be considered as having two aspects. The first, the travel flexibility, personal safety and privacy that cars provide, is independent of travel speeds. However, the second is speed-dependent, and car’s superior convenience arises mainly because cars are in most cities usually much faster door-to-door than competing travel modes (Moriarty and Honnery 2008). Only for commuting trips to or from the inner area of cities (or trips within this area itself) are other modes often faster.

We tend to ignore the fact that cars are allowed to travel at high speeds in urban areas, and in most cases are also allowed to drive through (and park in) the center of cities, despite high land prices and dense pedestrian flows. The speed limits allowed for road vehicles are quite arbitrary. In the city of Graz, Austria, they are 30 km/hr on all side-roads, and near centers such as schools and hospitals. Together these areas account for 80% of the total city area. Elsewhere in the city, the speed limit is 50 km/hr (Moriarty and Honnery 2012). In contrast, in Australian cities, the speed limit on arterial roads, even in fully built-up areas, is usually 70 km/h, and on freeways, 100 km/h.

If cars afford faster travel times in our cities, it is largely because we have allowed this high speed travel. The important point is that by deploying policies such as reductions in urban speed limits and parking space availability, road closures in the central city, and limits on further road space provision, it should be possible to greatly reduce the convenience we have granted urban cars, and so car travel itself, without the need to raise urban population densities. Comparing Asian with US cities provides a natural experiment for the effects of such restrictions on car travel. Table 1 shows that the lower provision of road and CBD parking space acts to lower average car speeds, and greatly raises the share of non-car trips for commuting. Only the four high-income Asian cities (Hong Kong, Seoul, Singapore, Tokyo) were considered for comparison. Except for CBD parking spaces, the data refer to the entire city areas.

Table 1. Transport-related parameters for US and Asian cities, 1990. Average for 13 US cities Average for 4 Asian cities Urban density (persons/ha) 14.2 175.8 Road provision (meters/capita) 6.9 1.5 CBD parking spaces/1000 jobs 468 72 Average car speed (km/h) 51.1 23.9 Average rail speed (km/h) 37.2 39.9 Transit work trips (%) 9.0 59.6 Walk/cycle work trips (%) 4.6 20.2 Total annual veh p-km/capita 16519 6143 Total annual veh MJ/capita 64351 13887 Source: Newman and Kenworthy (1999). A rival interpretation might be that the much higher density of the Asian cities better

explains the data. But Mindali et al. (2004) used multivariate statistical analysis to review the Newman and Kenworthy data, and concluded that there is ‘no direct impact of total urban density’ on transport energy consumption. Nor can city size explain the results: although the urban density of cities in a given country do correlate directly with population, US cities with populations equal to or greater than Singapore and Hong Kong still have far lower densities. These reduction measures could be variously justified by their beneficial impacts on traffic collision frequency and severity, petroleum consumption and imports, urban space provision, and on urban quality of life. Transport infrastructure costs would also be reduced.

Even if the above points are conceded, it could be argued that the much greater use of non-motorized and public transport in presently low transport energy cities is achieved at the expense of increased travel times. High mobility cities may have traded off the lower energy

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efficiency of private travel mainly for ‘travel-time efficiency’, which is simply the inverse of travel speed. Travel times are considered very important for urban transport; a major justification for new road-building works is the total travel time savings, expressed as monetary benefits (‘time is money’) in cost-benefit analyses.

But even with the existing bias in favor of car travel, the time-savings benefits are ambiguous, since faster modes of travel do not necessarily lower total daily travel times. Moriarty (2002) found that the historical shift from public to private transport as the dominant urban travel mode in Melbourne, Australia, was accompanied by a modest rise in daily per capita travel time outlays for the average resident. Travel speeds, as conventionally measured, did rise, but distance travelled (and energy use) by the average resident rose even more. Higher travel speeds did not lead to reduced total travel time. It is thus important to compare not just travel times for individual trips in a car-oriented transport system—as individual travellers themselves are likely to do—but also what overall daily or weekly travel times would look like in a city not organized around the car. Further, even for individual trips, travel time savings comparisons are again ambiguous, given that time spent on public transport or walking can fulfill other purposes. Public transport patrons can use their time for working or leisure activities such as reading, and non-motorized transport provides exercise.

A further, related, objection to massive modal shift could be made. Present private travel in OECD countries includes many trips that would be very expensive (in both money and energy terms) for public transport to duplicate, such as those late at night, or to thinly-settled rural areas. Either the scheduled services would have to be very infrequent to enable adequate occupancy rates, or demand responsive services (which could prove energy intensive) would be needed. Given this, it might be argued that shifting nearly all car travel to public transport would not reduce transport energy use or emissions significantly. However, a public transport and non-motorized system that replaced a car-based system would not necessarily duplicate the latter’s trip patterns. Trip-making patterns, and indeed per capita passenger-km levels, will be different for different dominant transport modes.

5. Discussion In Section 3 we argued that in a future growth economy, technical measures (fuel efficiency increases, more use of alternative fuels) cannot deliver the deep cuts needed. Hueting (2010), along with an increasing number of researchers (see for example, Schneider et al. 2010, Kallis 2011, Trainer 2012, and the contributors to two recent Special Issues in The Journal of Cleaner Production in 2010 and 2013), doubt that environmental sustainability can be attained if production, and thus GDP, continues to grow. Degrowth will therefore be necessary, they argue. Sekulova et al. (2013) define degrowth thus: ‘Degrowth can generally be defined as a collective and deliberative process aimed at the equitable downscaling of the overall capacity to produce and consume and of the role of markets and commercial exchanges as a central organising principle of human lives.’

A degrowth policy, and with it the need for deep cuts in both energy and GHGs, would evidently affect all sectors, not just transport. Indeed, Trainer (2012) has argued that it cannot be achieved ‘without replacing several of the fundamental structures and systems of consumer-capitalist society.’ Energy use and CO2 emissions are unlikely to decline ‘naturally’in growing economies: the decrease in national CO2 emissions observed in many OECD countries from 1990 to 2008 was largely caused by a rise in imports of energy and CO2 intensive manufactured imports from Asia (Peters et al. 2011). With lower industrial production and GDP, funds for R&D would be reduced. The cumulative production levels needed for learning curve cost reductions in new technology of all kinds would be greatly

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curtailed. Even if degrowth policies were implemented, uptake of non-fossil energy sources and energy efficient equipment could still be slower than in a business-as-usual growth economy. Excess capacity in fossil fuel generating plant would occur, slowing down the introduction of new RE electric capacity. Only in areas of production favored by degrowth—for example, public transport vehicles—could further technical efficiency gains be expected.

Since a conscious degrowth policy would deeply affect all sectors of the economy, the location of workplaces, the types of jobs available, the volume of retail sales, and so on, could all be expected to change. These changes will add to those advocated in Section 4.2: emphasizing accessibility rather than vehicular mobility; reversing present transport mode priorities to favor non-motorized over motorized travel; and favoring public over private vehicular transport. Nevertheless, the uncertainties in future urban activities make detailed long-term transport planning difficult.

It is difficult to imagine how degrowth, or the related transport changes advocated here, could be politically implemented at present. Travel reductions have occured in emergency situations such as petrol shortages, but travel levels soon revert to normal levels after the emergency is over. Nevertheless, as mentioned in Section 4, many OECD countries have seen declines in per capita surface transport passenger-km in recent years, often starting several years before the 2008 world financial crisis. For the U.K., Metz (2012) has argued that attitudes toward car ownership and travel are undergoing change, with fewer young people seeking driving licences. The high cost of fuels, vehicle ownership and parking, and congestion charging (such as that introduced in London in 2003), have all likely contributed to these changes. In London, all vehicle-km on major roads declined 8.7% between 2001 and 2011, even though it rose on major roads in Great Britain overall by 4.6% (UK National Statistics 2012). It could be that the declining availability of low-priced transport fuels will force steeper reductions in car travel, in advance of wider changes in the economy, as John Urry (2011) has argued. He even talked of a potential ‘de-mobilisation’ and ‘Autogeddon’,

while Millard‐Ball and Schipper (2011) asked whether ‘peak travel’ has already occurred.

6. Summary In the context of a global growth economy, with a huge latent demand for motorized travel in low-mobility countries, the best we can hope for from technical solutions is reductions in kg CO2-e (including well-to-wheels emissions) per vehicle-km. Only if car ownership was at or near saturation worldwide would such measures have a chance of delivering absolute cuts in transport GHG emissions. Even reductions per vehicle-km could be difficult to achieve if we have to rely increasingly on non-conventional oil sources such as tar sands or shale oil, because of their high input energy costs per liter of fuel delivered to the vehicle tank. But we need very large absolute reductions in GHGs, as well as oil consumption, and in a limited time frame.

The main problem with the current emphasis on technical solutions to our problems is that they direct attention away from other approaches. Greening passenger transport requires a re-think of present vehicle-centered approaches, and a focus on accessibility rather than vehicular mobility. Urban density increases have been advocated as a means of cutting transport demand, and with it fuel and emissions. But such an approach needs unacceptably large density increases for large travel reductions, and even if these could be implemented,

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would take many decades. A better approach is to adopt transport policies that lower the door-to-door speed advantage of car travel such as much lower speed limits, road closures, restricted vehicular access in the inner city, and restraints on parking. The level of travel reduction will depend on the severity of the policies adopted, just as they would for motoring cost increases. However the latter approach would be most inequitable in OECD countries.

This review has illustrated the use of non-technology driven approaches for passenger, especially urban, transport. If as many think, a combination of environmental and resource constraints places limits on future economic growth, similar approaches will be needed in other energy consumption sectors. It is at present difficult to see how deliberate degrowth policies could be introduced. Yet in a number of OECD countries, car travel per capita has been falling, a trend which preceded the 2008 global financial crisis. So even if policies de-emphasizing economic growth are still some time off, it is possible that the end of cheap transport fuels will soon lead to a rethink of approaches to green transport.

References Alvarez, R.A., Pacala, S.W., Winebrake, J.J., Chameides, W.L., Hamburg, S.P., 2012. Greater focus needed on

methane leakage from natural gas infrastructure. PNAS 109, 6435–6440. An, F., Gordon, D., He, H., Kodjak, D., Rutherford D., 2007. Passenger vehicle greenhouse gas and fuel

economy standards: A global update. Accessed on 30 Oct. 2012 at (http://www.theicct.org/passenger-vehicle-greenhouse-gas-and-fuel-economy-standards).

Andress, D., Das, S., Joseck, F., Nguyen, T.D., 2012. Status of advanced light-duty transportation technologies in the US. Energy Policy 41, 348–364.

Australian Bureau of Statistics (ABS), 2006. 2006 Census results CD-rom. Also results of earlier censuses. Australian Bureau of Statistics (ABS), 2011. Survey of Motor Vehicle Use: 12 months ended 31 october 2010.

ABS Catalogue No. 9208.0 Battersby, S., 2012. Running wild. New Sci. 7 July, 32-37. Boarnet, M.G., Houston, D., Ferguson, G., Spears, S., 2010. Land use and vehicle miles of travel in the climate

change debate: Getting smarter than your average bear. Fifth annual Land Policy Conference of the Lincoln Institute of Land Policy, Cambridge, MA, May 24-25. Accessed on 20 July 2012 at (http://economics.ucr.edu/spring11/Boarnet%20paper%20for%205%204%2011%20seminar.pdf).

BP, 2012. BP statistical review of world energy 2012. BP, London. Bureau of Infrastructure, Transport and Regional Economics (BITRE) (2012) Traffic Growth in Australia,

Report 127. Department of Infrastructure and Transport, Canberra, Australia. Campbell, C.J., 2012. Recognition of peak oil. WIREs Energy Environ. 1, 114–117 (doi: 10.1002/wene.7).

City Mayors, 2012. The largest cities in the world by land area, population and density. Accessed on 24 July 2012 at (http://www.citymayors.com/statistics/largest-cities-2007.html).

Cao, X., Patricia L. Mokhtarian, P.L., Handy, S.L., 2009. Examining the impacts of residential self-selection on travel behaviour: A focus on empirical findings. Transport Reviews 29(3), 359–395.

Cleveland, C.J., 2005. Net energy from the extraction of oil and gas in the United States. Energy 30, 769-782. Cullen, J.M. Allwood J.M., Borgstein E.H., 2011. Reducing energy demand: What are the practical limits?

Environ. Sci. & Technol. 45, 1711–1718. Dale M., Krumdieck S., Bodger P., 2011. Net energy yield from production of conventional oil. Energy Policy

39, 7095–7102. Davis, S.C., Diegel S.W., Boundy, R.G., 2012. Transportation Energy Data Book Edition 31. Accessed on 4

September 2012 at (http://cta.ornl.gov/data/tedb31/Edition31_Full_Doc.pdf). Dray, L., Schafer, A., Ben-Akiva, M., 2012. Technology limits for reducing EU transport sector CO2 emissions.

Environ. Sci. & Technol. 46, 4734−4741. Energy Information Administration (EIA), 2011. International Energy Outlook 2011. US Department of Energy,

Washington, DC. Felix, E., Tilley, D.R., 2009. Integrated energy, environmental and financial analysis of ethanol production from

cellulosic switchgrass, Energy, 34, 410–436. Geels, F.W., 2012. A socio-technical analysis of low-carbon transitions: Introducing the multi-level perspective

into transport studies. J. Transp. Geog. 24, 471–482. Giampietro M., Mayumi K., 2009. The Biofuel Delusion: The Fallacy of Large Scale Agro-biofuels Production.

Earthscan, London, U.K.

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

Global Fuel Economy Initiative (GFEI), 2011. International comparison of light-duty vehicle fuel economy and related characteristics, Working Paper 5/10. Accessed on 6 Nov. 2012 at http://www.globalfueleconomy.org/Documents/Publications/wp5_iea_fuel_Economy_report.pdf

Global Wind Energy Council (GWEC), 2012. Global Wind 2011 Report. GWEC, Brussels, Belgium. Gomiero, T., Paoletti, M.G., Pimentel, D., 2010. Biofuels: Efficiency, ethics, and limits to human appropriation

of ecosystem services. J. Agric. Environ. Ethics 23, 403–434. Hansen, J., Sato, M., Ruedy, R., 2012. Perception of climate change. PNAS 109, E2415–E2423. Hueting, R., 2010. Why environmental sustainability can most probably not be attained with growing

production. J. Cleaner Production 18, 525–530. International Council on Clean Transportation (ICCT), 2011. Global light-duty vehicles: fuel economy and

greenhouse gas emissions standards. Accessed on 5 Nov. 2012 at (http://www.theicct.org/info/documents/PVstds_update_apr2011.pdf).

International Energy Agency (IEA), 2012. Key world energy statistics 2012. IEA/OECD, Paris. Kahn Ribeiro, S., Kobayashi, S., Beuthe, M., 2007. Transport and its infrastructure. Ch 5 in: Metz, B.,

Davidson, O.R., Bosch, P.R., et al., editors. Climate change 2007: Mitigation. CUP, Cambridge, UK. Kallis, G., 2011. In defence of degrowth. Ecol. Econ. 70, 873–880. Karathodorou, N., Graham, D.J., Noland, R.B., 2010. Estimating the effect of urban density on fuel demand.

Energy Econ. 32, 86-92. Kennedy, C., Steinberger, J., Gasson, B., Hansen, Y., Hillman, T., Havránek, M., et al., 2009. Greenhouse gas

emissions from global cities, Environ. Sci. & Technol. 43, 7297–7302. Kenworthy, J., Inbakaran, C., 2011. Differences in transport and land use in thirteen comparable Australian,

American, Canadian and European cities between 1995/6 to 2005/6 and their implications for more sustainable transport. ATRF Proc., 28-30 September, Adelaide, Australia. Accessed on 16 January 2013 at (http://www.worldtransitresearch.info/cgi/viewcontent.cgi?article=5608&context=research).

Litman, T., Steele, R., 2012. Land use impacts on transport: How land use factors affect travel behavior. Accessed on 14 January 2012 at (http://www.ssti.us/wp/wp-content/uploads/2012/07/VTPI_2012_land_use+travel.pdf).

Metz, D., 2012. Demographic determinants of daily travel demand. Transport Policy 21, 20–25. Meyer, I., Kaniovski, S., Scheffran, J., 2012. Scenarios for regional passenger car fleets and their CO2

emissions. Energy Policy 41, 66–74.

Millard‐Ball A., Schipper, L., 2011. Are we reaching peak travel? trends in passenger transport in eight

industrialized countries. Transp. Rev. 31(3), 357–378. Mindali, O., Raveh, A., Salomon, I., 2004. Urban density and energy consumption: A new look at old statistics.

Transp. Res. Part A 38, 143–162. Mock, P., German, J., Bandivadekar, A., Riemersma, I., 2012. Discrepancies between type-approval and ‘real-

world’ fuel-consumption and CO2 values. ICCT Working Paper 2012-02. Accessed on 5 Nov. 2012 at http://www.theicct.org/sites/default/files/publications/ICCT_EU_fuelconsumption2_workingpaper_2012.pdf

Moriarty, P., 1998. Inequality in Australian cities. Urban Policy & Res. 16(4), 211-218. Moriarty, P., 2002. Household travel time and money expenditures. Road & Transp. Res. 11(4), 14-23. Moriarty, P., Beed, C., 1988. Transport characteristics and policy implications for four Australian cities. Urban

Policy & Res. 6(4), 171-80. Moriarty, P., Honnery, D., 2005. Determinants of urban travel in Australia. Proc. 28th ATRF, Sydney, 28-30

September. Moriarty, P., Honnery, D., 2008. The prospects for global green car mobility. J. Cleaner Production 16, 1717-

1726. Moriarty, P., Honnery, D., 2012. Reducing personal mobility for climate change mitigation. Chapter 51 in

‘Handbook of Climate Change Mitigation’, W.-Y. Chen, J.M. Seiner, T. Suzuki and M. Lackner (Eds.-in-chief), Springer, N.Y.

Newman, P., Kenworthy, J., 1989. Cities and automobile dependence: An international sourcebook. Gower, Aldershot, U.K.

Newman, P., Kenworthy, J., 1999. Sustainability and cities: Overcoming automobile dependence. Island Press, Washington, DC.

NGVA europe, 2012. Worldwide NGV statistics. Accessed on 3 September 2012 at (http://www.ngvaeurope.eu/worldwide-ngv-statistics).

MANUSCRIP

T

ACCEPTED

ACCEPTED MANUSCRIPT

O’Connor, J., 2004. Survey on actual service lives for North American buildings. Woodframe Housing Durability and Disaster Issues Conference, Las Vegas, October 2004. at (http://www.wolmanizedwood.com/Docs/Outdoor/SurveyonActualServiceLives.pdf).

Organization of the Petroleum Exporting Countries (OPEC), 2011. World oil outlook 2012. Accessed on 15 November 2012 at (http://www.opec.org/opec_web/static_files_project/media/downloads/publications/WOO2012.pdf).

Peters, G.P., Minx, J.C., Weber, C.L., Edenhofer, O., 2011. Growth in emission transfers via international trade from 1990 to 2008. PNAS 108, 8903–8908.

Rendall, S., Page, S., Reitsma, F., Van Houten, E., Krumdieck, S., 2011. Quantifying transport energy resilience: Active mode accessibility. Transportation Research Record: Journal of the Transportation Research Board 2242, 72–80.

Rockström, J., Steffen, W., Noone, K., et al., 2009. A safe operating space for humanity. Nature 461, 472-475. Schäfer A, Victor D., 2000. The future mobility of the world population. Transp. Res. A 34(3), 171-205. Schipper, L., Ng, W-S., Gould, B., Deakin, E, 2010. ‘Carbon in Motion 2050’ for North America and Latin

America. University of California at Berkeley Global Metropolitan Studies Final Report, March. Accessed on 30 Oct. 2012 at (http://metrostudies.berkeley.edu/pubs/reports/Carbon%20in%20Motion-UC-Final.pdf).

Schneider, F., Kallis, G., Martinez-Alier, J., 2010. Crisis or opportunity? Economic degrowth for social equity and ecological sustainability. Introduction to this special issue. J. Cleaner Production 18, 511–518.

Sekulova, F., Kallis, G., Rodríguez-Labajos, B., Schneider, F., 2013. Degrowth: from theory to practice. J. Cleaner Production 38, 1-6.

Statistics Bureau, 2013. Japan Statistical Yearbook 2013. Accessed on 18 January 2013 at (http://www.stat.go.jp/english/data/nenkan/index.htm#Contents). (Also earlier editions.)

Steemers, K., 2003. Energy and the city: Density, buildings and transport. Energy and Buildings 35, 3–14. Strahan, D., 2009. Scraping the bottom of the barrel. New Sci. 5 December, 34-39. Suzuki, T., Lee, S., 2012. Jobs–housing imbalance, spatial correlation, and excess commuting. Transp. Res. Part

A 46, 322–336. Tollefson, J., 2012. Air sampling reveals high emissions from gas field. Nature 482, 139-140. Trainer, E.F., 2012. De-growth: Do you realise what it means? Futures 44, 590–599. Tsao, C-C., E. Campbell, J.E., Mena-Carrasco, M., Spak, S.N., Carmichael, G.R., Chen, Y., 2012. Increased

estimates of air-pollution emissions from Brazilian sugar-cane ethanol. Nature Climate Change 2, 53-57. UK National Statistics, 2012. Region and Country Profiles: Key statistics. Accessed on 18 January 2013 at

(http://www.ons.gov.uk/ons/taxonomy/index.html?nscl=Travel+and+Transport). United Nations (UN), 2012. World urbanization prospects: The 2011 revision. Accessed on 3 August 2012 at

(http://esa.un.org/unpd/wup/index.htm). United States Census Bureau, 2012. The 2012 Statistical Abstract. Accessed on 15 January 2013 at

(http://www.census.gov/compendia/statab/). (Also earlier editions.) Urry, J., 2011. Does mobility have a future? Ch. 1 in: Grieco, M. and Urry, J., editors. Mobilities: New

Perspectives on Transport and Society. Ashgate, Farnham, U.K. Usón, A.A., Capilla, A.V., Bribián, I.Z., Scarpellini, S., Sastresa, E.L., 2011. Energy efficiency in transport and

mobility from an eco-efficiency viewpoint. Energy 36, 1916-1923. West, P.C., Gibbs, H.K., Monfreda, C., Wagner, J., Barford, C.C., Carpenter, S.R., Foley, J.A., 2010. Trading

carbon for food: Global comparison of carbon stocks vs. crop yields on agricultural land. PNAS 107, 19645–19648.

World Energy Council (WEC), 2011. Global Transport Scenarios 2050. WEC, London. Yu, C., Hien, W.N., 2006. Thermal benefits of city parks. Energy and Buildings 38, 105–120.

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• Technical solutions will not deliver needed transport energy reductions

• Travel reduction through acceptable land use changes are too small and slow

• De-growth might be necessary in OECD countries to achieve reductions

• Changes in transport behavior will be necessary

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Table 1. Transport-related parameters for US and Asian cities, 1990. Average for 13 US cities Average for 4 Asian cities Urban density (persons/ha) 14.2 175.8 Road provision (meters/capita) 6.9 1.5 CBD parking spaces/1000 jobs 468 72 Average car speed (km/h) 51.1 23.9 Average rail speed (km/h) 37.2 39.9 Transit work trips (%) 9.0 59.6 Walk/cycle work trips (%) 4.6 20.2 Total annual veh p-km/capita 16519 6143 Total annual veh MJ/capita 64351 13887 Source: Newman and Kenworthy (1999).