3.1. Introduction

In 1990, CO2 emissions from transport sector energy use amounted to about 1.25 Gt C--one-fifth of CO2 emissions from fossil fuel use (SAR II, 21.2.1). Other important GHG emissions from the sector include N2O from tailpipe emissions from cars with catalytic converters; CFCs and HFCs, which are leaked and vented from air-conditioning systems; and NOx emitted by aircraft near the tropopause (at this height, the ozone generated by NOx is a very potent GHG). World transport energy use grew faster than that in any other sector, at an average of 2.4% per year, between 1973 and 1990 (SAR II, 21.2.1).

GHG mitigation in the transport sector presents a particular challenge because of the unique role that travel and goods movement play in enabling people to meet personal, social, economic, and developmental needs (SAR II, 21.2.3). The sector may also offer a particular opportunity because of the commonality of vehicle design and fuel characteristics. Transport has many stakeholders, including private and commercial transport users, manufacturers of vehicles, suppliers of fuels, builders of roads, planners, and transport service providers. Measures to reduce transport GHG emissions often challenge the interests of one or another of these stakeholders. Mitigation strategies in this sector run the risk of failure unless they take account of stakeholder concerns and offer better means of meeting the needs that transport addresses. The choice of strategy will depend on the economic and technical capabilities of the country or region under consideration (SAR II, 21.4.7).

3.2. Global Carbon Emission Trends and Projections

Table 4 shows energy use by different transport modes in 1990, and two possible scenarios of CO2 emissions to 2050 (SAR II, 21.2). These two scenarios are used in this section as the basis for evaluating the effects of measures on GHG emissions. Energy intensity fell by 0.5- 1% per year in road transport between 1970 and 1990, and by 3- 3.5% per year in air transport between 1976 and 1990. Ranges of future traffic growth and energy-intensity reduction shown in the table are expected to be slower than in the past (SAR II 21.2.5). Most scenarios in the literature foresee a continuing reduction in growth rates for energy use whereas these two scenarios are based on constant growth rates; thus, the HIGH estimates in this table are much higher than IS92e for 2050. The LOW scenario in 2050 is about 10% below IS92c, and would be unlikely to occur without some change in market conditions (such as a sharp rise in oil prices) or new policies, for example to reduce air pollution and traffic congestion in cities.

The largest transport sector sources of GHG through to 2050 are likely to be cars and other light-duty vehicles (LDVs), heavy-duty vehicles (HDVs), and aircraft. Current annual percentage growth in all of these is particularly high in southeast Asia, while some central and eastern European countries are seeing a very rapid increase in car ownership. Two-wheelers, especially mopeds with two-stroke engines, are one of the fastest growing means of personal transport in parts of south and east Asia and Latin America, but account for only 2-3% of global transport energy use (SAR II, 21.2.4). These vehicles have very high emissions of local pollutants.

Annex I countries accounted for about three-quarters of global transport sector CO2 emissions in 1990. This share is likely to decline to about 60-70% by 2020 (SAR II, 21.2.2) and further by 2050, assuming continuing rapid growth in non-Annex I countries.

3.3. Technologies for Reducing GHG Emissions in the Transport Sector

Transport systems and technology are evolving rapidly. Although in the past this evolution has included reductions in energy intensity for most vehicle types, relatively little reduction occurred during the decade prior to 1996. Instead, recent technical advances mainly have been used to enhance performance, safety, and accessories (SAR II, 21.2.5). There is little or no evidence for any saturation of transport energy demand as marginal income continues to be used for a more transport-intensive lifestyle, while increasing value-added in production involves more movement of intermediate goods and faster, more flexible freight transport systems.

A number of technological and infrastructural mitigation options are discussed in the SAR (II, 21.3). Several are already cost-effective in some circumstances (i.e., their use reduces private transport costs, taking into account energy savings, improvements in performance, etc.). These options include energy-efficiency improvements; alternative energy sources; and infrastructure changes, modal shifts, and fleet management. The cost-effectiveness of these technical options varies widely among individual users and among countries, depending on availability of resources, know-how, institutional capacity, and technology, as well as on local market conditions.

3.3.1. Energy-Efficiency Improvements

Some energy-intensity reductions are cost-effective for vehicle operators, because fuel savings will compensate for the additional cost of more energy-efficient vehicles (SAR II, 21.3.1). Several studies have indicated that these potential savings are not achieved for a variety of reasons, in particular their low importance for vehicle manufacturers and purchasers relative to other priorities, such as reliability, safety, and performance. Many vehicle users also budget for vehicle operation separately from vehicle purchase, especially where the latter depends on obtaining a loan, so that they do not trade off the vehicle price directly against operating costs. Although fuel savings may not justify the time, effort, and risk involved for the individual or corporate vehicle purchaser, they could be achieved through measures that minimize or bypass these barriers. In cars and other personal vehicles, savings that are cost- effective for users in 2020 might amount to 10-25% of projected energy use, with vehicle price increases in the range $500-1,500. Larger savings in energy are possible at higher cost, but these would not be cost-effective (NRC, 1992; ETSU, 1994; DeCicco and Ross, 1993; Greene and Duleep, 1993).

The potential for cost-effective energy savings in commercial vehicles has been studied less than that in cars, and is estimated to be smaller--perhaps 10% for buses, trains, medium and heavy trucks, and aircraft--because commercial operators already have stronger incentives to use cost-effective technology (SAR II,

Energy-intensity reductions are possible beyond the level that is cost-effective for users; however, vehicle design changes that offer large reductions in energy intensity also are likely to affect various aspects of vehicle performance (SAR II, Achieving these changes would thus depend either on a shift in the priorities of vehicle manufacturers and purchasers, or on breakthroughs in technology performance and cost.

Where energy-intensity reductions result from improved vehicle body design, GHG mitigation may be accompanied by a reduction in emissions of other air pollutants, where these are not controlled by standards that effectively require the use of catalytic converters. On the other hand, some energy-efficient engine designs (e.g., direct fuel injection and lean-burn engines) have relatively high emissions of NOx or particulate matter (SAR II,

Changes in vehicle technology can require very large investments in new designs, techniques, and production lines. These short-term costs can be minimized if energy-efficiency improvements are integrated into the normal product cycle of vehicle manufacturers. For cars and trucks, this means that there might be a 10-year delay between a shift in priorities or incentives in the vehicle market, and the full results of that shift being seen in all the vehicles being produced. For aircraft, the delay is longer because of the long service life of aircraft, and because new technology is only approved for general use after its safe performance has been demonstrated through years of testing.

3.3.2. Alternative Energy Sources

On a full-fuel-cycle basis, alternative fuels from renewable energy sources have the potential to reduce GHG emissions from vehicle operation (i.e., excluding those from vehicle manufacture) by 80% or more (SAR II, At present, these fuels are more expensive than petroleum products under most circumstances, although vehicles operating on liquid biofuels can perform as well as conventional vehicles and manufacturing costs need be no higher in mass production. Widespread use of these fuels depends on overcoming various barriers, including the costs of transition to new vehicle types, fuel production and distribution technology, concerns about safety and toxicity, and possible performance problems in some climates. The widespread use of hydrogen and electricity in road vehicles poses technical and cost challenges that remain to be overcome.

Fossil fuel alternatives to gasoline [e.g., diesel, liquefied petroleum gas (LPG), compressed natural gas (CNG)] can offer 10-30% emission reductions per kilometer, and are already cost-effective for niche markets such as high-mileage and fleet vehicles, including small urban buses and delivery vans (SAR II, Several governments are encouraging the use of LPG and CNG because they have lower emissions of conventional pollutants than gasoline or diesel, but switching from gasoline to diesel can result in higher emissions of particulates and NOx. The use of hybrid and flexible-fuel vehicles may allow alternative fuels and electric vehicles to meet the mobility needs of a larger segment of vehicle users, but at a higher cost and with smaller GHG reductions than single-fuel vehicles (SAR II, 21.3.4). Alternatives to diesel are unlikely to be cost-effective for users of heavy-duty vehicles, and many will result in increased GHG emissions (SAR II, Nevertheless, a small but increasing number of urban buses and delivery vehicles are being fueled with CNG, LPG, or liquid natural gas (LNG) to reduce urban emissions of NOx and particulates. Alternatives to kerosene in aircraft are being tested, but are unlikely to be cost-effective in the near term (SAR II, Much of the political impetus for the use of alternative fuels has objectives other than GHG mitigation, such as improving urban air quality, maintaining agricultural employment, and ensuring energy security.

3.3.3. Infrastructure and System Changes

Urban density, urban and transport infrastructure, and the design of transport systems can all affect the distance people travel to meet their needs and their choice of transport modes (SAR II, 21.4.2). These factors also influence the volume of freight transport and the modes used. The extent of these various effects is controversial, and it should be noted that urban and transport infrastructure is usually designed predominantly for objectives other than GHG mitigation.

Traffic and fleet management systems have the potential to achieve energy savings on the order of 10% or more in urban areas (SAR II, 21.4.2). Energy use for freight transport might be reduced substantially through changes in the management of truck fleets. Modal shifts from road to rail may result in energy savings of 0-50%, often resulting in commensurate or greater GHG emission reductions, especially where trains are powered by electricity from non-fossil fuel sources (SAR II, 21.3.4, 21.4.2). The cost-effectiveness and practicality of freight transport by rail varies widely among regions and commodities (SAR II, 21.2.5). The long-term potential for rail freight may depend on the development of rail and intermodal technologies that can cope with a growing emphasis on flexibility and responsiveness.

3.4. Measures for Reducing GHG Emissions in the Transport Sector

A first step toward meeting climate objectives in the transport sector is to introduce GHG mitigation measures that are fully justified by other policy objectives. Such measures may increase the competitiveness of industry, promote energy security, improve citizens' quality of life, or protect the environment (SAR II, 21.4). In principle, the most economically efficient way to address all of these issues is by removing the subsidies that exist in some countries for road transport, and by introducing pricing mechanisms that reflect the full social and environmental cost of transport (SAR II, 21.4.5).

In practice, economically efficient measures such as road-user charges may be difficult to implement for technical and political reasons. Local circumstances demand local solutions, and the success of strategies may depend on their being designed:

  • With an understanding of the current system and its evolution
  • Including consideration of a wide range of measures
  • In consultation with stakeholders
  • Including monitoring and adjustment mechanisms (SAR II, 21.4.7).
  • This analysis cannot provide a global assessment, but considers ranges of possible effects of measures. It focuses on the three vehicle groups expected to be the largest sources of GHGs in 2020 (i.e., LDVs, HDVs, and aircraft).

    Annex I countries account for the vast majority of the world's vehicle fleets; developing countries in 1990 accounted for about a tenth of the world's cars. Meanwhile, almost all of the vehicles produced world-wide are either manufactured in Annex I countries or made to designs originating in those countries (SAR II, 21.2.4). Policies introduced in Annex I countries that affect vehicle technology are thus likely to have world-wide effects.

    3.4.1. Measures Affecting Light-Duty Road Vehicles and Urban Traffic

    Long-term management of GHG emissions from light-duty vehicles is likely to depend on implementing wide-ranging strategies involving several areas of policymaking and levels of government (SAR II, 21.4.1). These strategies might involve a variety of measures, including fuel economy standards (SAR II, 21.4.3), fuel taxes (SAR II,, incentives for alternative fuel use (SAR II, 21.3.3), measures to reduce vehicle use (SAR II, 21.4.2), and RD&D; into vehicle and transport system technology (SAR II, 21.3.6), some of which are evaluated in Table 5. The relative effectiveness of policies depends on national circumstances, including existing institutions and policies, and on underlying technology trends. Measures to reduce GHG emissions from cars are normally appropriate for other light-duty vehicles such as light trucks, vans, minibuses, and sports utility vehicles. These vehicle types increasingly are being used as personal vehicles, leading to higher GHG emissions. This increasing use could be encouraged if such vehicles are not subject to the same measures as cars.

    Many of the measures in Table 5 might be justified wholly or partly by objectives other than GHG mitigation. Fuel economy standards and feebates may be justified as means of overcoming market barriers that inhibit the uptake of cost-effective, energy-efficient technology. Increased fuel taxes also can have a range of social and environmental benefits, while generating revenue that can be recycled to meet priority needs in the transport sector or elsewhere, although they may also impose a welfare loss on some transport users.

    Governments are most likely to adopt some combination of measures. For example, fuel economy standards and incentives can result in a lower cost of driving--hence more traffic, unless implemented in conjunction with fuel taxes, road pricing, or other measures to discourage driving. Renewable energy supplies are more likely to be able to meet future transport energy needs if energy intensity and traffic levels are kept low. Thus, the effectiveness of incentives to purchase alternative fuel vehicles may be enhanced by taxes on conventional fuels, which provide incentives both to use alternative fuels and to reduce energy use.

    Policies developed at a local level, aimed at efficiently addressing the full range of local economic, social, and environmental priorities, may be among the most important elements of a long-term strategy for GHG mitigation in the transport sector (SAR II, 21.4.2). Measures include computerized traffic control; parking restrictions and charges; use of tolls, road pricing, and vehicle access restrictions; changing road layouts to reduce traffic speed; and improved facilities and priority in traffic for pedestrians, cyclists, and public transport.

    Infrastructure development is very expensive, and this cost is likely to be committed for a broad range of economic, social, environmental, and other reasons. There may be institutional barriers to integration of GHG mitigation objectives into decisionmaking processes, but doing so could have a range of benefits, perhaps leading to lower costs where non-motorized transport receives a higher priority than before, relative to motorized transport. Designing cities for non- motorized and public transport can lead to long-term economic benefits as the improved urban environment stimulates local business (SAR II, 21.4.2).

    Some of the best-known examples of strategies that have succeeded in reducing traffic and its environmental effects, including GHG emissions, have been implemented by the city-state of Singapore, the city of Curitiba in Brazil, and a number of European cities (SAR II, 21.4.6). These cities illustrate the importance of local initiative and integrated planning and market-based approaches in developing appropriate combinations of measures.

    A wide range of environmental and social benefits may come from local transport strategies to reduce traffic and improve non- motorized access (SAR II, 21.4.6), although such strategies may also result in welfare losses for some transport users.

    In the long term, changes in travel culture and lifestyle, combined with changes in urban layout, might lead to substantial reductions in motorized travel in North American and Australian cities. The potential reduction in west European cities is smaller (SAR II, 21.4.2). Some of the most important short-term opportunities for urban planning to affect long-term transport energy use is in countries with economies in transition and fast-developing countries, where the car is still a minority transport mode but is rapidly increasing in importance (SAR II, 21.4.2).

    3.4.2. Measures Affecting Heavy-Duty Vehicles and Freight Traffic

    Table 6 summarizes some possible effects of measures to reduce heavy-duty vehicle GHG emissions. Measures differ from those for light-duty vehicles because trucks vary more than cars in design and purpose, making it harder to design energy-intensity standards for them, although compulsory fitting of speed limiters and power-to-weight ratios can reduce energy use (SAR II, Meanwhile, commercial vehicle operators are relatively responsive to fuel prices in both their management of existing vehicles and their choice of new vehicles. A combination of fuel taxes and voluntary agreements, publicity, and incentives (e.g., in license fees) for the purchase of energy-efficient vehicles may be sufficient to encourage the uptake of technology improvements (SAR II,

    Studies in some countries have found that HDVs are subsidized more than LDVs, considering the high share of road repair costs allocable to HDVs. Efficient measures to reflect these costs to freight operators could increase the costs of road freight by 10-30% (SAR II, 21.4.5) and would achieve 10-30% reductions in freight traffic and associated GHG emissions (based on price elasticities in Oum et al., 1990). Other policies, such as the development of intermodal facilities to encourage the use of rail, often are advocated. Enhancing rail infrastructure may indeed be able to contribute to GHG mitigation, when combined with constraints on the use of road freight, and disincentives such as tolls (SAR II, 21.4.3). High use of rail is most practical for long hauls, so that such policies would be most effective in large countries or when internationally coordinated in regions with large numbers of small countries (SAR II, 21.2.4).

    3.4.4. Measures Affecting Aircraft 10  

    Table 7 summarizes the effects of a range of policies to reduce GHG emissions from aircraft. Large reductions in NOx emissions might be more politically feasible through aircraft engine standards (SAR II, and RD&D; funding, although the radiative impact of aircraft NOx is short-lived and highly uncertain and there could be tradeoffs between reduced NOx and fuel efficiency (SAR II,

    The Council of the International Civil Aviation Organization (ICAO) recommends that fuel used for international aviation should be tax- exempt (SAR II,, but does not preclude "charges" for environmental purposes. Some airports have landing fees related to aircraft noise levels, and environmental charges could extend to cover aircraft GHG emissions (e.g., through a fuel surcharge). International cooperation, at least at a regional level, could discourage airlines from selecting airports for refueling or as long- haul hubs on the basis of relative fuel prices.

    In the long term, substantial reductions in CO2 and NOx emissions from aircraft may depend on RD&D; along with market incentives to develop and introduce technologies and practices with lower energy intensity (SAR II, and fuels based on renewable sources (SAR II, At present, there are substantial institutional and technical barriers, including safety concerns, to the introduction of such technologies.

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