APPENDIX B
Contribution of U.S. Transportation Sector to Greenhouse Gas Emissions and Assessment of Mitigation Strategies

The body of this report describes how climate change is expected to impact the U.S. transportation sector and identifies ways in which this impact might be ameliorated. The committee’s charge also directed it to review what is known about the contribution of transportation to greenhouse gas (GHG) emissions:

Drawing heavily upon analyses already prepared, the study will summarize current and projected contributions of transportation to climate change and the potential effects, costs, and benefits of strategies to reduce transportation’s impact. This would include strategies, for example, that affect land use patterns, influence mode choice, and involve alternatively fueled or more efficient motor vehicles.

This appendix addresses this aspect of the committee’s charge.

HOW THE TRANSPORTATION SECTOR INFLUENCES CLIMATE CHANGE

Transportation vehicles emit GHGs when fuel undergoes combustion in their engines. The vast majority of these combustion-related emissions consist of carbon dioxide (CO2).1 But road transport vehicles also emit

1

 The U.S. Energy Information Agency’s annual publication Emissions of Greenhouse Gases in the United States provides estimates of transport sector emissions of CO2, CH4, and N2O. In 2003, CO2 accounted for 97 percent of the total, when each gas is converted into its global warming



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APPENDIX B Contribution of U.S. Transportation Sector to Greenhouse Gas Emissions and Assessment of Mitigation Strategies T he body of this report describes how climate change is expected to impact the U.S. transportation sector and identifies ways in which this impact might be ameliorated. The committee’s charge also directed it to review what is known about the contribution of transportation to greenhouse gas (GHG) emissions: Drawing heavily upon analyses already prepared, the study will summarize current and projected contributions of transportation to climate change and the potential effects, costs, and benefits of strate- gies to reduce transportation’s impact. This would include strategies, for example, that affect land use patterns, influence mode choice, and involve alternatively fueled or more efficient motor vehicles. This appendix addresses this aspect of the committee’s charge. HOW THE TRANSPORTATION SECTOR INFLUENCES CLIMATE CHANGE Transportation vehicles emit GHGs when fuel undergoes combustion in their engines. The vast majority of these combustion-related emissions consist of carbon dioxide (CO2).1 But road transport vehicles also emit 1 The U.S. Energy Information Agency’s annual publication Emissions of Greenhouse Gases in the United States provides estimates of transport sector emissions of CO2, CH4, and N2O. In 2003, CO2 accounted for 97 percent of the total, when each gas is converted into its global warming 210

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Contribution to Emissions and Assessment of Strategies 211 small amounts of nitrous oxide (N2O) and methane (CH4). Aircraft oper- ating at high altitudes emit not only nitrogen oxides (NOx) [which increases the rate of ozone production by speeding the oxidation of car- bon monoxide (CO) and CH4] but also water vapor [which generates contrails that, depending on the time of day they are produced, either reflect solar radiation back into space (daytime) or trap it (nighttime)] (IPCC 1999; see also Stuber et al. 2006). Transport activity is also associated with two additional categories of emissions: (a) those produced in the extraction, production, and distribu- tion of transport fuels and (b) those produced in the manufacture, distribution, and disposal of transport vehicles.2 A rough idea of the rela- tive significance of these additional categories of emissions can be obtained from life-cycle studies that attempt to track all emissions related to a vehi- cle and its fuel. One of the best known of these studies estimates that the life-cycle CO2 emissions generated by a 1996-vintage midsize U.S. passen- ger car using gasoline as its fuel total 263 g/km, of which the vehicle manufacturing cycle (including disposal) accounts for 18 g/km (6.8 per- cent); the fuel cycle, 49 g/km (18.7 percent); and fuel combustion, 196 g/km (74.5 percent) (Weiss et al. 2000, 5–8).3 In this appendix, the committee attempts to provide as comprehen- sive a picture as possible of transport-related GHG emissions. It was not feasible to include emissions from each life-cycle stage or emissions of each GHG gas; we do, however, take care to identify which emissions are included in the data presented. CURRENT AND PROJECTED TRANSPORT-RELATED GREENHOUSE GAS EMISSIONS According to the 2005 edition of the International Energy Agency (IEA) publication CO2 Emissions from Fuel Combustion, worldwide CO2 emis- potential. Nearly all the remainder was accounted for by N2O (U.S. Energy Information Administration 2004, 31, 49, 62). This publication provides no information on aerosols produced by transport activity, but these are believed to be relatively insignificant. 2 The second of these categories is of concern only with respect to road vehicles. The number of nonroad vehicles (locomotives, ships, and aircraft) is so small that the GHG emissions related to their manufacture, distribution, and disposal are minimal. 3 The report assumes 95 percent recycling of metals and 50 percent recycling of plastics. In the report, the emissions figures are stated in grams of carbon per kilometer. For consistency with the other emissions data in this appendix, the figures have been converted here to grams of CO2 per kilometer.

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212 Potential Impacts of Climate Change on U.S. Transportation sions from fuel combustion in 2003 totaled 25.0 billion tonnes (IEA 2005). The transport sector accounted for 5.9 billion tonnes, or 23.6 percent of this total (IEA 2005).4 Another IEA publication (IEA 2006) provides “ref- erence case” projections of emissions for 2050. According to that report, total CO2 emissions from fuel consumption in 2050 will be 57.6 billion tonnes (IEA 2006). Transport sector emissions will be 11.7 billion tonnes, or 20.3 percent of this total. The two IEA publications just cited do not provide a high level of modal detail. However, the World Business Council for Sustainable Development’s Sustainable Mobility Project (SMP) has published detailed modal estimates of emissions from fuel combustion for 2000 and projec- tions at 5-year intervals to 2050 (World Business Council for Sustainable Development 2004).5 The SMP also published estimates and projections of CO2, N2O, and CH4 emissions from the production and distribution of transport fuels. The SMP’s figures were generated by a model that was benchmarked to the IEA transport sector totals. Table B-1 shows the esti- mates and projections generated by this model. Light-duty passenger vehicles (LDVs), consisting of passenger cars, pickup trucks, sport utility vehicles (SUVs), and minivans, account for the largest share of transport-related emissions. This will continue to be the case even in 2050 if present trends continue. However, emissions from other modes, notably air transport and trucks used to haul freight, are extremely significant and are projected to grow faster than emissions from LDVs. The SMP report also provides estimates and projections of transport- related emissions by country/region. These are shown in Figure B-1. The United States is included in the region “OECD [Organisation for Economic Co-operation and Development] North America” along with Canada and Mexico. One notable feature of Figure B-1 is the differences in relative growth rates of emissions within different countries/regions. Generally speaking, These are emissions from fuel combustion. 4 The documentation for this model, as well as the model itself, can be found at www. 5 sustainablemobility.org. The SMP characterizes its projections as what might occur “if present trends continue.” For a description of what is meant by the phrase “if present trends continue,” see Box 2.1 in the SMP report (p. 27). The report also can be found at the web address just cited. The report draws on 2003 data, the most recent available at the time the report was published. This appendix, which draws heavily on the SMP report, uses 2003 data because it would have been impractical to update the data contained in the SMP report.

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Contribution to Emissions and Assessment of Strategies 213 TABLE B-1 World Transport Well-to-Wheels (Vehicle + Upstream) CO2-Equivalent Emissions by Mode (megatonnes) Year AAGR (%) Mode 2000 2025 2050 2000–2025 2025–2050 Freight + passenger rail 207 341 503 2.0 1.6 Bus 396 436 480 0.4 0.4 Air 733 1,487 2,583 2.9 2.2 Freight truck 1,446 2,423 3,582 2.1 1.6 Light-duty passenger vehicle 2,798 4,152 5,901 1.6 1.4 Two- and three-wheeler 110 209 313 2.6 1.6 Water 638 826 1,015 1.0 0.8 Total 6,328 9,874 14,378 1.8 1.5 Note: AAGR = annual average growth rate. Source: Data generated by the International Energy Agency/Sustainable Mobility Project (IEA/SMP) Spreadsheet Model. 14000.0 12000.0 Africa Latin America 10000.0 Middle East India Megatonnes 8000.0 Other Asia China 6000.0 Eastern Europe FSU OECD Pacific 4000.0 OECD Europe OECD North America 2000.0 0.0 2000 2005 2010 2015 2020 2025 2030 2035 2040 2045 2050 Year FIGURE B-1 Transport greenhouse gas emissions by region (all modes). (Source: Data generated by IEA/SMP Spreadsheet Model.)

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214 Potential Impacts of Climate Change on U.S. Transportation emissions from countries not presently members of the OECD are pro- jected to grow much more rapidly than emissions from countries that are members of the three OECD regions. The factors responsible for this faster growth are discussed in more detail below. IEA estimates that U.S. transport-sector emissions from fuel combus- tion in 2003 totaled 1.8 billion tonnes, of which road transport (LDVs, motorized two- and three-wheelers, buses, medium- and heavy-duty trucks) accounted for 85 percent. The U.S. Environmental Protection Agency (EPA) provides estimates having a greater level of modal detail (see Table B-2). Comparison of the figures from Table B-2 with those from Table B-1 implies that in 2003, U.S. transport emissions of CO2 from fuel combustion accounted for 30 to 31 percent of total world transport CO2 emissions from fuel combustion, depending on whether international avi- ation and marine bunkers are included.6 The emissions factors developed by the SMP for the production and distribution of each type of transport fuel suggest that including fuel cycle emissions would add another 17.5 percent to the U.S. total (and 15.0 percent to the world total). EPA does not publish projections of future emissions at a similar level of detail. And, as already noted, the SMP’s projections are for OECD North America (i.e., the United States, Canada, and Mexico). According to the SMP data in Figure B-1, OECD North American transport-related emissions will have fallen from 37 percent of the world transport-related total to 26 percent by 2050. This decline in share is accounted for not by any absolute reduction in North American emissions but by the much more rapid rate of growth projected for emissions in regions (other than the other two OECD regions) outside North America. STRATEGIES FOR REDUCING TRANSPORT-RELATED GREENHOUSE GAS EMISSIONS The charge to the committee quoted above recognizes that a range of possible approaches exist by which transport-related GHG emissions 6 “International aviation and marine bunkers” denotes fuel loaded on transport vehicles in the United States but consumed in international operations. Generally speaking, “international bunkers” are not included in national totals, though they are included in the world totals cited above. The IEA estimates that in 2003, the combustion of international aviation bunkers accounted for 359 million tonnes of CO2 emissions. The combustion of international marine bunkers is estimated to have accounted for 459 million tonnes of CO2 emissions.

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TABLE B-2 U.S. CO2 Emissions from Fossil Fuel Combustion in Transportation End-Use Sector, 2003 (Tg CO2 Eq.) Fuel Type Distillate Mode Fuel Oil Aviation Residual Natural Sharea Vehicle Type Gasoline (Diesel) Jet Fuel Gasoline Fuel Oil Gas LPG Electricity Mode Totala (%) Road vehicles 1,464.1 78.9 Automobiles 630.2 3.4 0.0 633.6 34.2 Light-duty trucks 460.9 17.6 0.0 0.3 478.8 25.8 Other trucks 39.6 301.1 0.5 341.2 18.4 Buses 0.3 8.0 0.6 0.0 8.9 0.5 Motorcycles 1.6 1.6 0.1 Rail 39.6 3.2 42.8 2.3 Waterborne 82.1 4.4 Ships and boats 17.0 29.5 46.5 2.5 Ships (bunkers) 6.0 18.6 24.6 1.3 Boats (recreational) 11.0 11.0 0.6 Aircraft 230.8 12.4 Commercial aircraft 122.8 122.8 6.6 Military aircraft 20.5 20.5 1.1 General aviation 9.4 2.2 11.6 0.6 Other aircraft 16.3 16.3 0.9 Aircraft (bunkers) 59.6 59.6 3.2 Pipeline 34.8 34.8 1.9 Fuel totala 1,166.6 369.7 228.6 2.2 48.1 35.4 0.8 3.2 1,854.6 100.0 Fuel sharea (%) 62.9 19.9 12.3 0.1 2.6 1.9 0.0 0.2 Note: Totals may not sum because of independent rounding. LPG = liquefied petroleum gas. a Includes aircraft and waterborne international bunkers. Source: USEPA 2005, Table 3-7.

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216 Potential Impacts of Climate Change on U.S. Transportation might be reduced. The committee believes that the best way of organiz- ing the present discussion of this range of approaches is through the use of the “ASIF decomposition.” The CO2 emissions from fuel combustion by transport vehicles can be characterized by the following equation: G = A∗Si∗Ii∗Fi,j where G = CO2 emissions from fuel combustion by transport; A = total transport activity; Si = modal structure of transport activity; Ii = energy consumption (fuel intensity) of each transport mode; and Fi,j = GHG emissions characteristics of each transport fuel (i = trans- port mode, j = fuel type). The product of the first two variables on the right-hand side of this equation, A and Si, is the demand for transport services provided by transport mode i. The product of the last two variables, Ii and Fi,j, is the GHG generated by each unit of transportation service provided by mode i using fuel type j.7 Historically, the primary driver of transport-related GHG emissions has been the growth of total transport activity (A). The primary offsetting factor has been a reduction in the energy required to produce each unit of transport services (I). However, improvements in transport energy effi- ciency have been overwhelmed by the increase in transport activity. Changes in the modal structure of transport activity (S) have tended to boost GHG emissions in two ways. First, activity has tended to shift from less energy-intensive transport modes (e.g., rail) to more energy-intensive modes (e.g., truck). Second, in some modes (e.g., LDVs), the load factor (the percentage of vehicle capacity actually utilized) has fallen sharply.8 Changes in the emissions characteristics of transport fuels (F) have had little impact one way or another. 7 This formulation was originally popularized by Lee Schipper. This particular version is taken from IEA (see IEA 2000, 22). 8 In both trucking and air transport, improvements in average load factors have tended to offset some of the impact of the inherently higher energy intensiveness of the mode. The energy intensiveness of the modes (I) has increased somewhat as a result. (It takes more energy to move heavier average loads.) But the increase in energy required is considerably less than proportional to the increase in load.

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Contribution to Emissions and Assessment of Strategies 217 80.0 70.0 Africa Trillions of Passenger-Kilometers Latin America 60.0 Middle East India 50.0 Other Asia 40.0 China Eastern Europe 30.0 FSU OECD Pacific 20.0 OECD Europe 10.0 OECD North America 0.0 2000 2005 2010 2015 2020 2025 2030 2035 2040 2045 2050 Year FIGURE B-2 Passenger transport activity by region. (Source: World Business Council for Sustainable Development 2004, Figure 2-2, p. 30.) Reducing the Volume of Transport Activity (A) or Altering the Modal Structure of Transport Activity (S) The SMP report projects that worldwide personal transport activity, which totaled 32.3 trillion passenger-kilometers (pkm) in 2000, will grow to 74.0 trillion pkm by 20509 (see Figure B-2). Worldwide goods transport activity (excluding waterborne),10 which in 2000 totaled 14.4 trillion tonne-kilometers (tkm),11 is projected to grow to 45.9 tkm (see Figure B-3). These projections imply average annual rates of growth of 1.7 percent for personal transport activity and 2.3 percent for goods transport activity (again excluding waterborne). Figures B-2 and B-3 also indicate that rates of growth of both personal and goods transport activity are likely to vary widely across countries/ Passenger-kilometer is defined as the transportation of one passenger a distance of 1 kilometer. 9 The SMP report does not project waterborne freight activity. According to the United Nations 10 Conference on Trade and Development (UNCTAD 2005), in 2000, world seaborne trade totaled 23.7 trillion tonne-miles, or 43.9 tonne-kilometers (tkm). Of this total, 41 percent was oil and oil products, 29 percent was the five main dry bulk commodities (including iron ore, coal, and grain), and 30 percent was other dry cargoes (including containerized cargoes). We assume that the “miles” reported by UNCTAD (2005) are nautical miles. If so, this means that in 2000, ocean shipping accounted for 75 percent of all tkm of freight carried. 11 Tonne-kilometer is defined as the transportation of 1 metric ton (tonne) of freight a distance of 1 kilometer.

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218 Potential Impacts of Climate Change on U.S. Transportation 50.0 45.0 Africa 40.0 Latin America Trillions of Tonne-Kilometers Middle East 35.0 India 30.0 Other Asia 25.0 China EasternEurope 20.0 FSU 15.0 OECD Pacific OECD Europe 10.0 OECD North America 5.0 0.0 2000 2005 2010 2015 2020 2025 2030 2035 2040 2045 2050 Year FIGURE B-3 Goods transport activity (excluding waterborne). (Note: Waterborne activity not available by country/region. According to the United Nations Conference on Trade and the Environment, in 2000, worldwide waterborne transport activity totaled 43.9 trillion tkm.) (Source: World Business Council for Sustainable Development 2004, Figure 2-5, p. 32.) regions, reflecting basic economic and demographic changes discussed below. At present, the majority of both personal and goods transport activity occurs within or between countries that are members of the OECD.12 Over the next half-century, however, transport activity is pro- jected to grow much more rapidly in those countries that are not presently OECD members. These higher growth rates, if achieved, imply that non- OECD personal transport activity will exceed OECD personal transport activity by about 2025. The crossover point for goods transport activity is likely to be even sooner—perhaps as early as 2015. Drivers of the Volume of Personal and Goods Transport Activity Numerous factors influence the rate of growth of personal and goods transport activity, but the following are especially important: (a) the level and rate of growth of real per capita income, (b) the rate of population 12 The OECD was formed in 1961 by the following countries: Austria, Belgium, Canada, Denmark, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, the Netherlands, Norway, Portugal, Spain Sweden, Switzerland, Turkey, the United Kingdom, and the United States. The following countries have since joined: Japan (1964), Finland (1969), Australia (1971), New Zealand (1973), Mexico (1994), the Czech Republic (1995), Hungary (1996), Poland (1996), the Republic of Korea (1996), and Slovakia (2000).

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Contribution to Emissions and Assessment of Strategies 219 25.0 Per Capita Personal Travel Activity (thousands of km) OECD North America 20.0 OECD Pacific 15.0 OECD Europe 10.0 Eastern Europe FSU 5.0 Middle East Other Asia Latin America India China Africa 0.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 Per Capita Real Income (thousands of US$, Purchasing Power Parity Basis) FIGURE B-4 Per capita personal travel activity versus per capita real income. (Source: Data generated by IEA/SMP Spreadsheet Model.) growth, (c) the share of population residing in urban areas, and (d) the spatial organization of urban areas (also called “urban form”). In addi- tion, a potentially salient factor is the impact of telecommuting and the Internet on travel demand. Level and Rate of Growth of Real per Capita Income Transportation activity both drives and is driven by the level and rate of growth of real per capita income. This should not be surprising. Transportation services are a major enabler of economic growth, and as people become wealthier, they find more reasons to travel. Figure B-4 shows the relationship between real gross domestic product (GDP) per capita and per capita personal travel in 2000 for the countries/regions included in the SMP report.13 In 2000, the average resident of an OECD country traveled 5.7 times as many kilo- meters per year as did the average resident of a non-OECD country—a slightly lower ratio than that between the average real per capita incomes of the two country groupings. 13 Similar data for goods transport activity are not provided because the information on waterborne origin–destination pairs needed to assign that important transport activity to countries/regions is lacking.

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220 Potential Impacts of Climate Change on U.S. Transportation 3.0% Projected Change in per Capita Personal Transport Demand China 2.5% Eastern Europe FSU 2.0% Latin America 1.5% India OECD Europe 1.0% Other Asia OECD North OECD Pacific 0.5% America Africa 0.0% Middle East -0.5% 0.0% 0.5% 1.0% 1.5% 2.0% 2.5% 3.0% 3.5% 4.0% 4.5% Projected Change in Real Gross Domestic Product per Capita (Purchasing Power Parity Basis) FIGURE B-5 Projected change in real per capita personal transport demand versus projected change in real gross domestic product per capita (purchasing power parity basis), 2000–2050. (Source: Data generated from IEA/SMP Spreadsheet Model.) Figure B-5 shows the relationship between the projected rate of change in real GDP per capita and the projected rate of change in per capita per- sonal travel over the period 2000–2050. Note the difference in the relative positions in the two exhibits of the three OECD regions and those non- OECD countries/regions in which economic growth is projected to grow the most rapidly. Given the relationship between real per capita income growth and per capita personal (and probably also goods) transport activity, it is obvious that if the former were slower, so would be the latter. However, most peo- ple (especially those living in countries where real per capita GDP is relatively low today but is projected to grow rapidly) would find highly unpalatable a strategy of deliberately slowing growth in real GDP per capita in order to slow the growth of travel activity. This does not mean that the link between real per capita income growth and per capita travel activity is immutable. But it does mean that if this link is to be weakened,

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256 Potential Impacts of Climate Change on U.S. Transportation atmosphere by the growing of the biomass. But under plausible assumptions, net WTT CO2 emissions for biomass-derived fuels can still be negative. • The production process for some biofuels (e.g., ethanol from corn) generates coproducts that can displace other products that require energy to produce and whose production emits CO2. How these “coproduct credits” are allocated has a major impact on a biofuel’s costs, the energy required to produce it, and its WTT CO2 emissions (Farrell et al. 2006). • The production of transport fuels from nonpetroleum fossil car- bon sources (e.g., coal or natural gas) generates substantial CO2 emissions. However, if these emissions can be sequestered, the WTT emissions from the production of these fuels can be reduced to nearly zero. Analysts differ on how each these factors should be treated in “scoring” the WTT emissions characteristics of different transport fuels produced by different processes from different primary energy sources. Therefore, anyone reviewing the literature on this topic can expect to encounter a range of estimates. The important thing now universally acknowledged is that WTT emissions must be incorporated into any estimates of future transport-related CO2 emissions. Fueling Infrastructure A vast supply infrastructure has developed to deliver petroleum-based transport fuels to the vehicles that utilize them. As noted earlier, motor vehicles can use some alternative fuel blends (e.g., E5 and E10) without major modifications either to their engines or to their fuel systems. The same is true of the current fuel supply infrastructure. Today’s petroleum product pipelines routinely carry gasoline, diesel fuel, jet fuel, and propane. They also can carry “mild” blends of gasoline and biofuels (such as E5 and E10). But they cannot carry blends consisting of a majority of biofuels (such as E85) or 100 percent ethanol. The only gaseous transport fuel carried by pipeline is natural gas. Other gaseous transport fuels (in particular, hydrogen) would require dedicated pipelines. Another very important part of the transport fuel infrastructure is the fueling stations that actually deliver fuel to vehicles. Most of these are

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Contribution to Emissions and Assessment of Strategies 257 not directly connected to a pipeline. Instead, they are supplied by tank trucks that haul fuel from a distributing point (that is connected to a pipeline) to individual fueling stations. One of the most formidable challenges facing any new transport fuel would be the establishment of an infrastructure capable of distributing it widely. The enormous fixed costs involved in establishing such an infrastructure mean it would not be established without assurance that the demand for the products it would transport would be forthcoming. Yet the vehicles that would be the source of this demand would not be built and purchased without assurance that fuel to power them would be available. Efforts are being made in some states to establish “hydrogen high- ways.” These are routes along which enough hydrogen refueling stations have been established to permit drivers of hydrogen-fueled vehicles to travel on them. These stations are supplied by tanker trucks. While this could help build initial demand for hydrogen as a transport fuel, it is not a long-term solution to the fuel infrastructure problem. HOW MUCH AND OVER WHAT TIME PERIOD MIGHT TRANSPORT-RELATED GHG EMISSIONS BE REDUCED? This appendix has described a wide range of technological and non- technological means of reducing transport-related GHG emissions. In this final section, the committee attempts to indicate how much transport-related GHG emissions might be reduced given the trends thus far described. As stated at the outset, the fundamental challenge is to reduce the emissions produced per unit of transportation services provided more rapidly than the demand for transportation services grows. While it may be possible to reduce the rate of transportation demand growth some- what without harming economic growth unacceptably, the committee is aware of no forecast that projects that transportation demand will fail to grow relatively rapidly in the decades ahead, especially in many of the world’s less developed countries. The bulk of the responsibility for reduc- ing emissions will therefore fall on improved vehicle technologies and low-carbon or carbon-free fuels. There is considerable uncertainty about what it might cost to com- mercialize and widely disseminate many of the more advanced vehicle

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258 Potential Impacts of Climate Change on U.S. Transportation technology and fuel solutions. Given what is known about projected demand growth, however, it is possible to simulate what might be feasi- ble trajectories of advances in vehicle technology and fuel substitution. To obtain a better sense of the potential impact of various technolo- gies and fuels in reducing transport-related GHG emissions, the SMP conducted a number of simulations using its spreadsheet model. The benchmark was the SMP reference case projection showing total trans- port-related CO2 emissions doubling between 2000 and 2050, with most of the growth in emissions occurring in the countries of the developing world. While other analyses have examined this issue for individual developed countries or regions, to the committee’s knowledge, the SMP was the first to examine it for the world as a whole. In these simulations, the focus was on total road transport. The exer- cise did not examine the technical or economic feasibility of any of the actions being simulated. It was intended merely to help the SMP under- stand the impact on GHG emissions from road vehicles if the actions described were taken. This enabled the SMP to compare its results with those of other studies that likewise did not consider technical or economic feasibility in deriving their results. Single-Technology Simulation The SMP began by examining the impact of single technologies on CO2 emissions from road transport worldwide. Figure B-13 shows results for five such technologies—dieselization, hybridization, fuel cells, “carbon- neutral” hydrogen, and biofuels. It was assumed that each power train technology would achieve as close to 100 percent global sales penetration as possible given the characteristics of the technology and that each fuel would become as close to 100 percent of the global road transport fuel pool as its characteristics would permit. The SMP emphasized that these single-technology examples were purely hypothetical. It is highly unlikely in practice that any single tech- nology would achieve 100 percent penetration. Also, the examples cannot be added together. Differences in the timing of the implementation of these technologies and fuels in the developed and developing worlds were largely ignored. For both diesels and advanced hybrids, it was assumed that 100 per- cent sales penetration would be reached by 2030 and that these technologies

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Contribution to Emissions and Assessment of Strategies 259 12 Gigatonnes CO2-Equivalent GHGs 10 Reference Case 8 Diesels Hybrids 6 Fuel Cells (hydrogen from natural gas) Fuel Cells (zero-carbon 4 hydrogen) Advanced Biofuels (all road vehicles) 2 0 2000 2010 2020 2030 2040 2050 FIGURE B-13 Hypothetical potential of individual technologies to lower road transport well-to-wheels GHG emissions relative to the SMP reference case. (Source: World Business Council for Sustainable Development 2004, Figure 4.7, p. 113.) would be used in LDVs and medium-duty trucks.36 In the case of fuel cell vehicles, it was assumed that 100 percent sales penetration would be reached by 2050.37 It was also assumed that the hydrogen used in these vehicles would be produced by reforming natural gas and that carbon sequestration would not be involved. The estimate of the impact of car- bon-neutral hydrogen was generated by changing the WTT emissions characteristics of the hydrogen used in the fuel cell case just described. To focus on the impact of biofuels, it was assumed that these fuels would be used in a world road vehicle fleet similar in energy use characteristics to the SMP reference fleet. Diesel internal combustion engine technology (using conventional diesel fuel) was assumed to have an 18 percent fuel consumption benefit compared with the prevailing gasoline internal 36 A very high proportion of heavy trucks and buses are already diesel powered. The SMP assumed that hybrid technology would not see significant use in heavy-duty over-the-road trucks and buses because of their operating characteristics. Public transport buses are already being viewed as prime candidates for hybridization. These were not included in the SMP’s calculation, but their omission makes relatively little difference in the results. 37 The SMP made the same assumptions concerning the types of vehicles to which fuel cells might be applied as it did for hybrids.

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260 Potential Impacts of Climate Change on U.S. Transportation combustion engine technology during the entire period. The fuel con- sumption benefit relative to gasoline internal combustion engine technology was assumed to be 36 percent for diesel hybrids, 30 percent for gasoline hybrids, and 45 percent for fuel cell vehicles. From this single-technology assessment, it is evident that even if implemented worldwide, diesels and hybrid internal combustion engines fueled with conventional gasoline and diesel fuel or fuel cells fueled with natural gas–derived hydrogen could no more than slow the growth in road transport CO2 emissions during the period 2000–2050. Only the use of carbon-neutral hydrogen in fuel cells and advanced biofuels in inter- nal combustion engine–powered vehicles could largely or totally offset the increase in CO2 emissions produced by the growth in road travel dur- ing the period 2000–2050. This does not mean that vehicle energy use characteristics are irrele- vant. They might not have a major impact on the trajectory of road vehicle GHG emissions over the very long term, but they would have a major impact on the amount of low-carbon or carbon-neutral fuel that would have to be produced to power the world’s road vehicle fleet. This means they could have a very important impact on the cost of signifi- cantly reducing GHG emissions from road vehicles.38 On the basis of these results, the SMP concluded that it is only through a combination of fuel and power train solutions that significant CO2 reduction can be attained. No single-technology pathway merits selection as the sole long-run solution. Combined-Technology Simulation Since the substantial reduction of CO2 emissions from road vehicles is likely to depend on the widespread adoption of several advanced vehicle and fuel technologies, as well as other factors, the SMP decided to exam- ine the combined impact of several actions, including the following: • Fuels that are carbon neutral (defined by the SMP as ones that reduce WTW CO2 emissions by at least 80 percent); • Power trains that are highly energy efficient; 38 The fuel economy benefit relative to gasoline internal combustion engine technology was assumed to be 36 percent for diesel hybrids, 30 percent for gasoline hybrids, and 45 percent for fuel cell vehicles.

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Contribution to Emissions and Assessment of Strategies 261 • A change in the historical mix-shifting trend to larger vehicle cat- egories; and • Improved traffic flow and other changes in transport activity resulting from better integration of transport systems, enabled, at least in part, by information technology. The SMP set an illustrative target of reducing annual worldwide CO2 emis- sions from road transport by half by 2050. This is equivalent to a decline in yearly CO2 emissions of about 5 gigatonnes from levels that the SMP refer- ence case projects would otherwise be reached and, by coincidence, returns annual road vehicle CO2 emissions in 2050 to about their current levels. For illustrative purposes, the CO2 reduction target was divided into six increments. The timing and size of each increment are not fixed and ultimately would be decided on the basis of sustainability and investment choices at the national, regional, and global levels. The purpose of the analysis was to illustrate what might be achieved if ambitious changes were made beyond those in the SMP reference case, with no judgment as to cost or the probability of each step being taken. Increment 1. Dieselization: It was assumed that dieselization of LDVs and medium-duty trucks would rise to around 45 percent globally by 2030 (that is, to about current European levels). Diesel engines were assumed to consume about 18 percent less fuel (and emit 18 percent less CO2) than current gasoline internal combustion engines. Increment 2. Hybridization: It was assumed that the hybridization (gasoline and diesel) of LDVs and medium-duty trucks would increase to half of all internal combustion engine vehicles sold by 2030. Gasoline hybrids were assumed to consume an average of 30 percent less fuel than current gasoline internal combustion engines, and diesel hybrids were assumed to consume an average of 24 percent less fuel than current diesels.39 Increment 3. Conventional and advanced biofuels: It was assumed that the quantity of biofuels in the total worldwide gasoline and diesel pool would rise steadily, reaching one-third by 2050. Conventional biofuels (those yielding a 20 percent CO2 unit efficiency benefit) were capped at 39 It is generally acknowledged that, because of the diesel’s initial superior energy efficiency, any additional benefit from hybridizing a diesel is likely to be smaller than that from hybridizing a gasoline engine.

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262 Potential Impacts of Climate Change on U.S. Transportation 5 percent of the total pool. The balance was assumed to be advanced bio- fuels (those yielding at least an 80 percent CO2 unit efficiency benefit).40 Increment 4. Fuel cells using hydrogen derived from fossil fuels (no carbon sequestration): It was assumed that mass market sales of LDVs and medium-duty trucks would start in 2020 and rise to half of all vehi- cle sales by 2050. It also was assumed that fuel cell–equipped vehicles consume an average of 45 percent less energy than current gasoline inter- nal combustion engines. Increment 5. Carbon-neutral hydrogen used in fuel cells: It was assumed that hydrogen sourcing for fuel cells would switch to centralized production of carbon-neutral hydrogen over the period 2030–2050 once hydrogen LDV fleets had reached significant penetration at the country level. By 2050, 80 percent of hydrogen would be produced by carbon- neutral processes. The first five increments reflect the inherent properties of different vehicle technologies and fuels. Actual reductions in CO2 emissions will be determined not only by these properties but also by the mix of vehicles purchased by consumers and businesses and by how these vehicles are used on a daily basis. To reflect these two factors, two more increments were included. Increment 6. Additional improvement in fleet-level vehicle energy efficiency: The SMP reference case projects an average improvement in the energy efficiency of the on-road LDV fleet of about 0.4 percent per year, with new vehicle sales showing an average 0.5 percent per year improve- ment in fuel economy. The improvement potential embodied in actual vehicles is around 1.0 percent per year, but about half of this potential improvement is offset because of vehicle purchasers’ preferences for larger and heavy vehicles. In developing this increment, the SMP assumed that preferences relating to the mix of vehicles chosen by purchasers and the performance of these vehicles would change somewhat, leading to an additional 10 percent average annual in-use improvement relative to the reference case (i.e., average annual fleet-level improvement would rise from about 0.4 percent to about 0.6 percent). 40 This implies that these advanced biofuels are either gasoline from lignocellulosic sugar fermentation or diesel from biomass gasification/Fischer–Tropsch synthesis.

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Contribution to Emissions and Assessment of Strategies 263 Increment 7. A 10 percent reduction in emissions due to better traf- fic flow and other efficiencies in road vehicle use: It was assumed that the gap between on-road energy-use performance and the technological improvements embodied in vehicles would narrow. How might this hap- pen? For one thing, there are a number of opportunities relating to the increased use of information technology in transport systems that might enable the better management of travel demand. Improved routing infor- mation might permit trips to be shortened, while improved information about road conditions might reduce the amount of time motorists spend in their vehicles while idling in traffic. For another thing, more accurate and current information about when public transport vehicles will arrive and how long they will take to get to their destinations might encourage additional use of public transport. Individually, none of these improve- ments would be major, and almost certainly there would be offsets. But in combination, the SMP assumes that such factors could produce an additional 10 percent reduction in road vehicle CO2 emissions. Figure B-14 shows the results of the SMP combined-technologies analysis just described. It confirms the impression conveyed by the three single-technology analyses discussed above that the widespread adoption of a combination of vehicle and fuel technologies (plus other factors) would be required to return 2050 CO2 emissions from road vehicles to their 2000 level. SUMMARY Any global warming that will be experienced during the next several decades will largely be the result of GHG emissions that have already occurred. As the main body of this report points out, regardless of what else it might do, America’s transport sector will have to adjust to the con- sequences of this warming. But the transport sector in general, and America’s transport sector in particular, is a significant source of GHG emissions. If future warming is to be limited, GHG concentrations in the atmosphere must be stabilized. This will require reducing GHG emis- sions not merely to below what they might otherwise be if present trends were to continue but to well below current levels. The transport sector will have to contribute to this reduction. This appendix has identified several approaches by which transport- related GHG emissions might be reduced. A common characteristic of

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264 Potential Impacts of Climate Change on U.S. Transportation 12 Gigatonnes CO2-Equivalent GHGs 10 8 6 4 2 0 2000 2010 2020 2030 2040 2050 Diesels (LDVs) Hybrids (LDVs and MDTs) Biofuels (80% low GHG sources by 2050) Fuel Cells (fossil hydrogen) Fuel Cells (80% low-GHG hydrogen by 2050) Mix Shifting Yielding 10% Vehicle Efficiency Improvement 10% Vehicle Travel Reduction (all road vehicles) Remaining GHGs FIGURE B-14 Combined-technology case. (Source: Adapted from World Business Council for Sustainable Development 2004, Figure 4.11, p. 117.) these approaches is that they take considerable time to be fully effective. This means that if transport-related GHG emissions are to be reduced to below their current levels by 2050, steps must be taken now to begin to implement certain of these approaches. REFERENCES Abbreviations BTS Bureau of Transportation Statistics IEA International Energy Agency IMO International Maritime Organization IPCC Intergovernmental Panel on Climate Change UN United Nations

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266 Potential Impacts of Climate Change on U.S. Transportation Stuber, N., P. Forster, G. Rädel, and K. Shine. 2006. The Importance of the Diurnal and Annual Cycle of Air Traffic for Contrail Radiative Forcing. Nature, Vol. 441, No. 7095, June 15, pp. 864–867. UN. 1999. The World at Six Billion. Population Division, Department of Economic and Social Affairs, Oct. 12. www.un.org/esa/population/publications.sixbillion/ sixbillion.htm. Accessed Jan. 30, 2008. UN. 2003. World Urbanization Prospects: The 2003 Revision. Population Division, Department of Economic and Social Affairs. www.un.org/esa/population/ publications/wup2003/2003wup.htm. Accessed Jan. 30, 2008. UN. 2005. World Population Prospects: The 2004 Projection. Population Division, Department of Economic and Social Affairs, Feb. UNCTAD. 2005. Review of Maritime Transport 2005. www.unctad.org/Templates/ WebFlyer.asp?intItemID=3588&lang=1. Accessed Jan. 30, 2008. U.S. Energy Information Administration. 2004. Emissions of Greenhouse Gases in the United States. DOE/EIA-0573. U.S. Department of Energy. www.eia.doe.gov/oiaf/ 1605/archive/gg05rpt/index.html. Accessed Jan. 30, 2008. USEPA. 2005. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2003. EPA- 430-R-05-003. Washington, D.C., April 15. Weiss, M. A., J. B. Heywood, E. M. Drake, A. Schafer, and F. F. AuYeung. 2000. On the Road in 2020: A Life-Cycle Analysis of New Automobile Technologies. Energy Laboratory Report MIT EL 00-003. Cambridge, Mass., Oct. World Business Council for Sustainable Development. 2004. Mobility 2030: Meeting the Challenges to Sustainability. Sustainable Mobility Project, Geneva, Switzerland. www.wbcsd.org/web/mobilitypubs.htm. Accessed Jan. 30, 2008.