Global Warming on the Road

Global Warming on the Road

                John DeCicco and Freda Fung
                     ENVIRONMENTAL DEFENSE

                   WITH THE ASSISTANCE OF
                            Feng An
Cover image: Corbis.

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The complete report is available online at
           Executive summary                                        iv

           Introduction                                              1

           Methodology and assumptions                               4

           Carbon emissions from automobiles on the road             6

           Beyond the carbon tally                                  13

           Conclusions                                              21

           Appendix A: Stock modeling methodology and assumptions   22

           Notes                                                    27

           References                                               30

Executive summary

           For most Americans, the automobile is                 portionate impact: U.S. cars are driven
           an essential part of daily life. It has shaped        further each year and burn more fuel
           our culture and our landscape. The in-                per mile than the international average.
           dustries that build and serve cars form a             The United States has 5% of the world’s
           key part of our economy. The automobile               population and 30% of the world’s auto-
           is not without its faults, but they often             mobiles, but it contributes 45% of the
           are concealed by the styling, performance             world’s automotive CO2 emissions.
           and other features that make today’s                     In 2004, U.S. cars and light trucks
           vehicles so desirable. Still, when a                  emitted 314 million metric tons of
           product is so widely used, its faults can             carbon-equivalent (MMTc). That equals
           add up to massive unwanted side effects.              the amount of carbon in a coal train
               Consider global warming. Motor                    50,000 miles long—enough to stretch 17
           vehicles play a major part in what                    times between New York and San Fran-
           scientists call the most serious environ-             cisco. In fact, the amount of CO2 emitted
           mental problem the world faces. The                   from oil used for transportation in the
           automobile’s main contribution comes                  United States is similar to the amount
           from the carbon dioxide (CO2) emitted                 from coal used to generate electricity.
           as the engine burns fuel.
               The greenhouse gas pollution that
           causes global warming comes from                      America’s ‘rolling carbon’
           numerous sources. Any single contribu-                This report details, for the first time,
           tion may seem small in proportion to the              the global warming pollution emitted
           world total, but collectively it becomes a            in the course of America’s daily driving.
           problem of vast scale. To address a prob-             It represents a complete picture of the
           lem of such vast scale requires interna-              nation’s “rolling carbon,” from the latest
           tional agreements and national policies.              luxury SUV cruising through an upscale
           But making good on such commitments                   suburb to the oldest pickup truck bump-
           will require changes in how we manage                 ing along a rural lane.
           every activity that contributes to the                    Many policy-related reports focus on
           problem. How much should we cut, and                  emissions from new vehicles, since new
           where? To answer this question, we need               vehicle sales are regularly reported in
           a clear picture of which sources con-                 detail. Here, using national statistics on
           tribute most to global warming.                       how long vehicles last and how far they
                                                                 are driven as they age, we examine the
                                                                 CO2 emissions from all personal vehicles,
           The disproportionate impact                           both new and used. This analysis allows us
           of U.S. cars and light trucks                         to answer questions such as, “How much
           Automobiles—by which we mean                          carbon is emitted by all the Ford-built cars
           personal motor vehicles, including light              now in use? From all the Hondas?” It also
           trucks such as pickups, SUVs and vans                 enables us to estimate the CO2 emissions
           as well as sedans and wagons—emit                     from all the sport-utility vehicles (SUVs)
           roughly 10% of global CO2 emissions                   in use, from all the midsize cars, and so
           from fossil fuels, which are the main                 on—that is, according to vehicle class.
           form of greenhouse gas pollution.                         Table ES1 summarizes on-road car-
           American automobiles have a dispro-                   bon emissions by vehicle class in 2004.

Rolling stock carbon emissions by vehicle class, 2004
Vehicle class           Carbon emissions (MMTc)                   Carbon emissions share
Small cars                            77                                      25%
SUVs                                  67                                      21%
Pickups                               60                                      19%
Midsize cars                          54                                      17%
Vans                                  29                                       9%
Large cars                            26                                       8%
Cars                                157                                       50%
Light trucks                        157                                       50%
Overall                             314                                      100%

Perhaps surprisingly, small cars (com-            plants. Next were pickup trucks, which
pacts, subcompacts and two-seaters)               collectively emitted 60 MMTc in 2004.
were responsible for the most carbon
emissions, amounting to 77 MMTc.
Small cars once had been the dominant             Car companies vs. electric
segment by sales; given the longevity of          companies: a comparison
vehicles, many of them remain on the              Table ES2 gives the breakdown by car
road today. Thus, despite their higher            company, which shows that automakers’
than average fuel economy, small cars             shares of rolling carbon follow historical
still accounted for the largest share of          market shares, led by GM. These results
rolling carbon emissions as of 2004.              are highlighted in Figure ES1, which
    This situation illustrates the relative       shows the quantity of carbon emitted by
durability of automobiles: In terms of            each automaker’s products compared to
usage, the U.S. light vehicle stock now           the carbon emissions of major electric
has a “half-life” of roughly eight years;         power companies. Car companies are
in other words, 50% of vehicles are               on a par with—and some even higher
replaced within that time. It takes               than—electric utilities in terms of the
16 years for the fleet to be 90% replaced         carbon emissions associated with the
in terms of the carbon emitted during             use of their products.
driving. In short, the choices made                  These estimates indicate that products
regarding new vehicles influence emis-            made by each of the Big Three—GM,
sions for many years to come.                     Ford and DaimlerChrysler—emitted
    SUVs represent the second largest             more carbon in 2004 than the country’s
portion of rolling carbon. They soon              largest electric utility, American Electric
will be the main source of automotive             Power (AEP). GM’s products emitted
CO2 emissions, having overtaken small             99 MMTc, and Ford’s emitted 80
cars in terms of market share in 2002.            MMTc, nearly twice AEP’s 41 MMTc.
Their impact will be all the greater due          DaimlerChrysler’s cars and light trucks
to their lower than average fuel economy.         in use emitted 51 MMTc. The total
As of 2004, all the SUVs on the road in           CO2 emissions from Big Three auto-
the United States emitted 67 MMTc,                mobiles in 2004 was comparable to the
an amount equivalent to the CO2                   total from the top 11 electric companies.
spewed by 55 large coal-fired power               And the global warming pollution from

vehicles made by Toyota (the fourth                        both cases, their carbon emissions
among automakers) edges out that from                      include the impacts of long-lived
the Tennessee Valley Authority (the                        products and equipment. The quantity
third among electric companies).                           of each sector’s emissions also is deter-
   Electric utilities and automakers may                   mined by a number of actors, including
seem like apples and oranges, but in fact                  end-users such as consumers and busi-
they make a suitable comparison. In                        nesses. For example, AEP’s CO2 emis-

Rolling stock carbon emissions by automaker, 2004
Manufacturer                       Carbon emissions (MMTc)                  Carbon emissions share
GM                                               99                                    31%
Ford                                             80                                    25%
DaimlerChrysler                                  51                                    16%
Toyota                                           27                                     9%
Honda                                            17                                     6%
Nissan                                           15                                     5%
Volkswagen                                        5                                     2%
Hyundai                                           4                                     1%
Mitsubishi                                        4                                     1%
BMW                                               3                                     1%
Kia                                               2                                     1%
Subaru                                            3                                     1%
Others                                            4                                     1%
Big Three                                       230                                    73%
Overall                                         314                                   100%

Carbon emissions of major automakers’ products vs. major electric
producers in the United States, 2004

             General Motors                                                              99
                         Ford                                                  80
            DaimlerChrysler                                       51
     American Electric Power                                 41
         Southern Company                                  37
                       Toyota                    27
   Tennessee Valley Authority                    26
                                                                  Major automakers’ products
                       Honda                17                    Major electric producers
                         Xcel               17
                     Ameren                 17
                     Cinergy               16
                   Dominion                15
        Edison International               15
            Progress Energy                15
                      Nissan               15
                                   0       20              40          60     80       100      120
                                                       Carbon emissions (MMTc)

Source: Table 1 and CERES et al. (2006).

sions are the result of the electricity              Total U.S. car and light truck VMT in
consumed in homes, offices, schools                  2004 amounted to 2.6 trillion miles.
and other power-using facilities in their           • Fuel use rate, or the amount of fuel
service area. Decisions by state and local            consumed per mile, which is the
officials are also important in both cases,           inverse of fuel economy. The fuel
through regulation of electric utility                economy of the U.S. automobile stock
services and rates on one hand, and                   averaged 19.6 mpg in 2004, implying
through transportation infrastructure and             an average fuel use rate of 51 gallons
land use planning on the other. More-                 per 1,000 miles of driving.
over, greenhouse gas pollution from both
sectors is influenced by the carbon in-             • Fuel carbon content, or the amount of
tensity of their fuel supply. While each              greenhouse gases emitted per gallon of
utility has its own mix of fuels, overall             fuel consumed. Counting only the CO2
utility emissions reflect the fact that 54%           directly released when fuel is burned,
of U.S. electricity comes from coal. Auto-            this factor amounts to 5.3 pounds of
mobile fuel essentially all comes from oil.           carbon per gallon of gasoline.

                                                    These three factors combined result in
The three-legged stool propping                     the 314 MMTc emitted by U.S. auto-
up emissions                                        mobiles in 2004.
Because automotive CO2 emissions are                   Among these factors, only decreases
influenced by many different decision               in fuel use rate (achieved by increasing
makers, finding opportunities to cut car-           fuel economy) have served to partially
bon entails looking at the factors behind           limit CO2 emissions. Fuel carbon con-
emissions. Figure ES2 illustrates the three         tent has not significantly changed,
main factors propping up rolling carbon:            reflecting the tenacity of oil as a useful
                                                    resource and the barriers facing alterna-
• Travel demand, or the amount of driv-
                                                    tive fuels. And many forces drive travel
  ing, which is commonly measured as
                                                    demand, all of them serving to push
  annual vehicle miles of travel (VMT).
                                                    auto sector CO2 emissions upward.

Three main factors behind rolling
carbon                                              Managing automotive rolling
                                                    Ultimately, cutting auto sector CO2 emis-
         Vehicle CO2 emissions                      sions will require attention to all three
                                                    legs of the stool. Thus, policy discussions
                                                    regarding transportation and climate are
                                                    typically framed around the question of
                                                    how to change travel demand, fuel econ-
                                                    omy or fuel type. A key challenge, how-
                                                    ever, is that each factor is the product of
                                                    decisions made by many actors. In addi-
                                                    tion to consumers, automakers and others
                                                    involved in the auto market, total auto
    Travel                        Fuel              sector CO2 emissions are influenced by
   demand       Fuel use rate    carbon             the energy industry as well as by the
                                                    many interests and levels of government

that shape land use, infrastructure and              zero. Better information on emissions,
other parts of the transportation system.            new evaluation tools and education are
    The magnitude of the automotive                  needed to enable all actors to understand
global warming problem and the com-                  how their decisions impact emissions.
plexities of the associated decision making             This report seeks to aid that process.
suggest a need to recast the question.               By underscoring the magnitude of auto-
Instead of asking “What policies are                 motive CO2 emissions, it highlights the
required to address the factors that prop            need to break the problem down into
up automobile carbon emissions?” deci-               manageable pieces. Consideration can
sion makers can ask “What policies can               then be given to opportunities to reduce
motivate each actor to address the aspects           carbon by tackling each piece of the
of emissions that they can influence?”               larger problem. Such a carbon manage-
Such a view shifts the focus from tech-              ment paradigm would enable each actor
nical factors and how they are deter-                to address the emissions each influences,
mined to individual actors and the parts             complementing existing policy strategies
of the problem they each can control.                defined around the technical factors that
    For some major actors, such as auto-             characterize total emissions. A city
makers, how much they can address emis-              government, for example, can change
sions is limited by other players. The               the emissions associated with its trans-
ability to increase fuel economy by re-              portation operations. It might do this
designing vehicles depends in part on                by carrying out its functions with less
the extent to which consumers make                   driving, increasing the efficiency of its
fuel economy a priority. Nevertheless, it            vehicles or using low-carbon fuels.
is implausible that automakers (or other                Exactly how to define a set of carbon
actors) have no ability to lower carbon              management policies appropriate for
emissions. Similarly, while individual               the auto sector is a subject for future
consumers cannot themselves redesign                 research as well as an important topic
cars (or develop new fuels or reshape                for discussion by everyone who holds a
land use), their scope of influence is not           stake in the car-climate problem.


               America’s cars are one of the world’s           enable us to answer questions such as
               largest sources of global warming pollu-        “What portion of CO2 emissions is
               tion. Our personal vehicles—from the            associated with pickup trucks?” or
               Mini Cooper to the Hummer and every-            “What portion of CO2 emissions is
               thing in between—emitted 314 million            represented by all Toyota vehicles on
               metric tons of carbon-equivalent                U.S. roads?” The results also underscore
               (MMTc) annually as of 2004.1 That               the scope of the car-carbon problem and
               equals the amount of carbon in a coal           show how long it takes for changes in
               train 50,000 miles long, enough to              the characteristics of new car sales to
               stretch 17 times between New York               influence the overall carbon emissions
               and San Francisco.2 In the United               from the auto sector.
               States, in fact, the amount of global              The approach taken here is similar
               warming pollution from oil used for             to that of our previous reports4 on auto-
               transportation is similar to that from          motive carbon burdens, referring to the
               coal used for electric power generation.3       annual CO2 emissions associated with a
                  Such comparisons can help Ameri-             given population of vehicles. However,
               cans understand the extent of our car-          while our Automakers’ Corporate Carbon
               bon problem, and they also help us              Burdens reports calculated CO2 emis-
               think about how to solve it. Emissions          sions as annual averages over the ex-
               from power plants depend on decisions           pected lifetime of a series of new model
               by power companies, but also on deci-           year vehicles, this report addresses the
               sions made by businesses and consumers          emissions from all vehicles (new and
               who choose and use electrical equip-            used) on the road in a given year. This
               ment and appliances. Similarly, auto-           particular analysis has never been done
               mobile emissions depend not only on             before. We present the results for 2004,
               automakers and fuel suppliers, but also         the most recent year for which sufficient
               on decisions by businesses and con-             data are available.5 The results depend
               sumers who choose vehicles, and by              not only on vehicle characteristics (such
               local, state and federal officials who          as fuel economy) but also on the extent
               oversee America’s transportation system         of driving. Thus, these “rolling carbon”
               and land use. Whether it is an issue of         estimates reflect both the number of
               primary energy resources (fossil or             vehicles in use and how many miles they
               otherwise), how the fuels are converted         are driven each year. The carbon emis-
               and distributed to consumers, or how            sions from model year 2004 new auto
               efficiently the fuels are used through          sales represent 10% of the emissions
               choices of technology and infrastruc-           from all automobiles on the road.
               ture, the interlocking nature and sheer            As the statistics assembled in this
               magnitude of carbon emissions implies           report show, the carbon emissions
               a shared task.                                  from all General Motors’ vehicles on
                  This report provides a detailed snap-        the road as of 2004 were more than
               shot of carbon emissions from the “roll-        double those from America’s largest
               ing stock” of all U.S. cars and light           electric generating company, American
               trucks on the road in 2004. We report           Electric Power (AEP). In fact, the
               results both by automaker and market            CO2 emissions of the Big Three—
               segment. The statistics compiled here           GM, Ford, DaimlerChrysler—each

exceeded those of AEP, and the emis-                          magnified because of their lower than
                                     sions associated with most major auto-                        average fuel economy.
                                     makers are comparable to or larger than                          Figure 1 places these estimates in
                                     those from the largest electric utilities                     a global context. Figure 1(a) breaks
                                     in the country.                                               down global fossil fuel CO2 emissions
                                        Perhaps even more surprising, the                          by major energy end-use in 2003.
                                     small car market segment (including                           Worldwide, automobiles (cars and
                                     compacts, subcompacts and two-seat                            other light-duty vehicles) emitted 680
                                     sports cars) produced the most global                         MMTc in 2003, about 10% of global
                                     warming pollution in 2004, simply                             CO2 emissions from fossil fuels.6 Oil,
                                     because so many of them remain on the                         coal, natural gas and related fossil
                                     road. The small-car carbon tally reflects                     resources account for 84% of all human-
                                     the longevity of vehicles, underscoring                       caused CO2 emissions (including other
                                     how decisions about the CO2 emissions                         major sources such as deforestation).
                                     rate of new vehicles will affect the                          CO2 is the dominant greenhouse gas
                                     amount of global warming pollution for                        (GHG, the term for any form of air
                                     years to come. SUVs had the second                            pollution that contributes to global
                                     largest share of CO2 emissions. While                         warming). It accounts for 72% of all
                                     their sales grew rapidly over the past 15                     human-caused GHG emissions. Thus,
                                     years, SUVs only overtook small cars in                       the light duty vehicle slice in Figure 1(a)
                                     terms of new car market share in 2002.                        represents an estimated 6% of all global
                                     SUVs soon will become the dominant                            warming pollution.7
                                     source of global warming pollution on                            Figure 1(b) breaks down global light
                                     America’s roads, and their impact will be                     vehicle CO2 emissions by country or

Global fossil carbon emissions by economic sector

                   1(a). Global carbon emissions by sector                                  1(b). Light duty vehicle carbon emissions
                            (6,814 MMTc in 2003a)                                                           by regionb
                                                                                                       (680 MMTc in 2003a)
                               Other sectorsc
                                                                                                      OECD              OECD
                Residential                              Industry                                                       Pacific
                                                           18%                                        Europe
                    8%                                                                                 21%               9%
                                                                                                                                  Former Soviet Union
                                                                                                                                  and Eastern Europe
                                                                                      Canada                                               Other Asia
                                                                                    and Mexico                                                 2%
     Electricity                                                     Light duty                                                              India
                                                                      vehicles          7%
      and heat                                                                                                                                1%
                                                                        10%                                                                Middle East
                                                                                                                                        Latin America
                                                               Other                                                                    2%
                                                           transportation                                     United States
                                                                14%                                               45%

These estimates include only CO2 emissions from fossil fuel use, and so exclude emissions from biofuel use or deforestation.
    Global emissions by sector are estimates for 2003 from IEA (2005). Global light-duty vehicle CO2 emissions for 2003 are projections from WBCSD (2004).
    Light duty vehicle emission shares by region are estimates for 2000 from WBCSD (2004).
    Other sectors include commercial, public services, agriculture and energy industries other than electricity and heat production.

major region as of 2000. U.S. cars and       because our vehicles are driven more
light trucks—the subject of this             than those in the rest of the world; the
report—are 45% of this total. The 202        11,000 miles per year average for U.S.
million automobiles on America’s roads       automobiles is about 29% greater than
in 2000 represent 30% of the estimated       the global average of 8,500 miles per
683 million automobiles (light duty          year.9 U.S. automobiles also consume
vehicles) in use worldwide that year.8       more fuel, emitting about 15% more
The U.S. share of automotive CO2             CO2 per mile than the average light
emissions is disproportionately high         duty vehicle globally.10

Methodology and assumptions

                                                                 Characterizing rolling stock CO2                                                      (g/mi) prior to 2000, corresponding
                                                                 emissions involves data on new vehicle                                                to an average on-road fuel economy of
                                                                 sales plus statistics on how long vehicles                                            20 mpg (similar to the actual on-road
                                                                 last and how much they are driven as                                                  average in recent years). If the CO2
                                                                 they age. To perform this analysis, we                                                emissions rate of new vehicles were
                                                                 use what is termed a stock model: a                                                   halved, down to 220 g/mi (correspond-
                                                                 computer-based accounting framework                                                   ing to a doubling of on-road fuel econ-
                                                                 that calculates fuel consumption and                                                  omy to 40 mpg) in 2000, the effect would
                                                                 CO2 emissions for various groupings of                                                not be fully reflected in the rolling stock
                                                                 vehicles. Given the sales volumes and                                                 until 2025. The gradual change in the
                                                                 fuel economy of a group of new vehicles                                               stock average CO2 emissions rate
                                                                 in a given year and previous years, the                                               reflects the slow turnover of vehicles;
                                                                 model computes the CO2 emissions rate                                                 lower-emitting new vehicles gradually
                                                                 of all such vehicles remaining on the                                                 replace older vehicles as they are driven
                                                                 road in the given year.                                                               less and then retired. However, progress
                                                                    Figure 2 illustrates how a stock model                                             is more rapid at first; 90% of the lower
                                                                 works, showing what would happen if                                                   CO2 emissions rate is achieved within
                                                                 the CO2 emissions rate of new cars sud-                                               16 years, even though it takes approxi-
                                                                 denly were cut in half as of model year                                               mately another decade for the oldest
                                                                 2000. The left graph shows the CO2                                                    vehicles to be completely replaced.
                                                                 emissions rate of the new fleet; the right                                               For our stock model, new vehicle
                                                                 graph shows the resulting impact on                                                   characteristics are obtained from federal
                                                                 the rolling stock emissions rate. In                                                  sales and fuel economy data, covering cars
                                                                 this simplified example, we assume an                                                 and light trucks of up to 8,500 pounds
                                                                 initially constant new fleet average CO2                                              gross vehicle weight (GVW). The
                                                                 emissions rate of 440 grams per mile                                                  stock turnover parameters, including

How the rolling stock responds to a cut in the new fleet CO2 emissions rate

                                               500                                                                                           500
   New fleet CO2 emissions rate (grams/mile)

                                                                                                     Stock CO2 emissions rate (grams/mile)

                                                                                                                                                                             Stock CO2 emissions
                                               400                                                                                           400                             rate drops gradually
                                                                                                                                                                                 over 25 years

                                               300                           New fleet CO2                                                   300
                                                                             emissions rate
                                                                             halved in 2000

                                               200                                                                                           200

                                               100                                                                                           100

                                                 0                                                                                             0
                                                 1970   1980   1990   2000     2010    2020   2030                                             1970    1980    1990   2000      2010   2020    2030

age-dependent vehicle survival proba-            the roughly 6 pounds of CO2 and other
bilities and usage rates, are also based         greenhouse gases emitted upstream
on government statistics. We calibrated          would bring the total, full fuel cycle emis-
our fuel use (and therefore CO2 emis-            sions to 25.3 pounds per gallon.13
sions) calculation to the most recently             While developing our vehicle stock
available data on total light duty vehicle       model, we reviewed the models used by
fuel use, ensuring that our total rolling        several government agencies and research
carbon estimate matches national                 institutes, including the Department of
statistics on the auto sector’s share of         Energy’s VISION and NEMS (Energy
U.S. CO2 emissions. We performed                 Information Administration) models,
sensitivity analyses to examine the              the Stockholm Environment Institute’s
effects of different vehicle survival and        LEAP model and EPA’s MOVES
usage parameters, confirming that our            model. VISION, LEAP and NEMS
estimates of manufacturer and vehicle            use approaches similar to the one we
segment shares are insensitive to changes        adopted, estimating stock carbon emis-
in such parameters.                              sions based on vehicle sales, fuel econ-
   We report the CO2 emissions (given            omy and stock turnover rate. They are
on a carbon-mass equivalent basis)               more complex, however, in that they are
released directly from fuel combustion           designed to calculate future stock changes
by the car—in other words, only the              that reflect numerous hypothetical alter-
CO2 coming from the tailpipe. How-               natives and couple the calculations to
ever, the tailpipe is not the only source        a broader energy modeling framework,
of greenhouse gases associated with each         neither of which are needed for our pur-
gallon of motor fuel consumed. Addi-             poses. EPA’s MOVES model combines
tional CO2 and other greenhouse gases            vehicle-specific, second-by-second emis-
are released when crude oil is extracted         sions calculations with travel activity
and shipped, when it is refined into             data to project stock fuel consumption,
gasoline or diesel fuel, and when these          allowing users to generate results for
motor fuels are distributed through              smaller geographic areas (e.g., at the
pipelines, barges and tanker trucks, even        county level) and in smaller temporal
before they go into a vehicle’s fuel tank.       units (e.g., by time of day). Although we
These upstream emissions add about               did not run these other models, we con-
31% to the global warming impact of              firmed the consistency of our stock
each gallon of gasoline burned in the            modeling results by comparing them
United States and about 23% to each              to published results from NEMS and
gallon of diesel fuel.11 The CO2 directly        MOVES. Appendix A provides further
released when burning gasoline amounts           detail on our stock model and the
to 19.4 pounds per gallon.12 Counting            assumptions behind it.

Carbon emissions from automobiles on the road

                            Our stock model tallies enable us to             (model year 2004) vehicles.15 In other
                            break down, by automaker and vehicle             words, the average older vehicle on the
                            class, the 314 MMTc emitted by all of            road actually burns less fuel and emits
                            the passenger cars and light trucks up to        less carbon than the average new
                            8,500 lbs gross vehicle weight (GVW)             vehicle. This situation reflects the fact
                            on U.S. roads in 2004.                           that new fleet fuel economy has been
                                                                             falling since 1988 due to the market
                                                                             shift from cars to light trucks. A com-
                            Rolling stock impacts of major                   parison of rolling stock vs. new fleet
                            automakers                                       carbon burden shares by automaker is
                            Table 1 lists our rolling stock results by       given in Figure 3. It shows that the
                            automaker, including estimates of the            distribution of CO2 emissions has
                            number of vehicles in service, their             been shifting away from the Big Three
                            average on-road fuel economy, average            toward other firms who are gaining
                            CO2 emissions rate, and contribution to          market share.
                            overall carbon emissions.14 These values             Vehicles built by the “Big Six”—
                            for the 2004 on-road stock can be com-           General Motors (GM), Ford,
                            pared to those for model year 2004 new           DaimlerChrysler, Toyota, Honda and
                            sales to illustrate the trends as older          Nissan—made up an estimated 92%
                            vehicles are replaced by newer ones. For         of the on-road light vehicle stock as
                            example, the overall stock on-road fuel          of 2004. With their historically leading
                            economy of 19.6 mpg is greater than              market shares, the Big Three (GM,
                            the 19.3 mpg overall average for new             Ford and DaimlerChrysler) alone

Light vehicle stock, fuel consumption, and carbon emissions by automaker, 2004
                        ROLLING STOCK AS OF 2004 (ALL VEHICLES NEW AND USED)                MY2004 (NEW FLEET ONLY)

                   Vehicle     On-road        Fuel     Carbon    Vehicle    Carbon     On-road                  Carbon
                  population fuel economy consumption emissions population emissions fuel economy Market        burden
Manufacturer      (millions)     (mpg)       (Mbd)     (MMTc)     share      share       (mpg)    share          share
GM                   64.4         19.2         2.68         98.6     31.6%        31.4%       18.9     27.5%    28.0%
Ford                 49.8         18.6         2.17         80.0     24.4%        25.5%       17.4     18.6%    20.6%
DaimlerChrysler      30.4         18.0         1.39         51.3     14.9%        16.3%       17.8     14.4%    15.6%
Toyota               18.6         21.6         0.74         27.1      9.1%         8.6%       21.3     13.2%    11.9%
Honda                13.3         24.2         0.47         17.3      6.5%         5.5%       23.2      8.7%     7.2%
Nissan               10.0         20.8         0.40         14.6      4.9%         4.6%       19.3      6.1%     6.1%
Volkswagen            3.7         22.7         0.14          5.1      1.8%         1.6%       21.6      2.3%     2.0%
Hyundai               2.8         23.8         0.10          3.8      1.4%         1.2%       22.0      2.7%     2.4%
Mitsubishi            3.0         21.8         0.12          4.3      1.5%         1.4%       22.4      0.9%     0.8%
BMW                   2.0         19.7         0.09          3.3      1.0%         1.0%       20.0      1.9%     1.8%
Kia                   1.3         21.0         0.06          2.2      0.6%         0.7%       20.0      1.7%     1.6%
Subaru                2.0         22.4         0.07          2.7      1.0%         0.9%       21.6      1.0%     0.9%
Others                2.5         19.1         0.10          3.8      1.2%         1.2%       19.0      0.9%     1.0%
Big Three           144.6         18.7         6.24       229.9      71.0%        73.2%       18.1     60.5%    64.2%
Overall             203.7         19.6         8.53       314.2     100.0%      100.0%        19.3    100.0% 100.0%

Stock vs. new fleet carbon burden shares by automaker, 2004

    General Motors
                                                       On-road stock
       Volkswagen                                      New fleet
                 0%       5%       10%           15%        20%        25%   30%     35%
                                            Carbon burden share

accounted for 71% of the stock, com-                 Ford has the second largest share of
pared to their 60% share of the 2004             carbon emissions. Its vehicles comprise
new vehicle market. Automakers’ shares           24.4% of the rolling stock and 25.5% of
of rolling stock carbon emissions closely        the stock carbon burden, amounting to
track their respective shares of the on-         80 MMTc in 2004. In Ford’s case, the
road vehicle population, with differences        shift to SUVs during the 1990s pulled
due to different average fuel economy            down their overall average fuel economy
levels and different mixes of older and          more than GM’s. Ford’s own reporting
newer vehicles on the road.                      of CO2 emissions from its vehicles is
    GM, which for many years has                 given on a global, rather than U.S. basis,
been the biggest automaker both in               and Ford did not provide an estimate in
the United States and globally, had an           its report to DOE’s Voluntary Report-
estimated stock share of 31.6%, with             ing of GHG Program, so direct com-
64 million light vehicles in 2004. The           parison is difficult. In its Corporate
average fuel economy of all GM cars              Citizenship Report 2003–04, Ford
and light trucks on the road was                 estimated that all the greenhouse gases
19.2 mpg, slightly lower than the over-          (CO2 and other GHGs, including
all average of 19.6 mpg.16 As seen in            refrigerants) emitted by Ford vehicles
Table 1, however, GM’s estimated share           on the road worldwide, including light
of overall rolling CO2 emissions, 31.4%,         and heavy duty vehicles, amounted to
is slightly lower than its share of the          109 MMTc in 2000.19
vehicle population.17 Thus, GM’s rolling             DaimlerChrysler follows in third
carbon amounted to 99 MMTc in 2004.              place, accounting for 14.9% of the roll-
This estimate compares well with the             ing stock and for 16.3% of stock carbon
93 MMTc estimate for 1999 based on               burden. That amounts to 51 MMTc,
information that GM supplied for the             a level greater than that from any U.S.
U.S. voluntary GHG reporting initiative          electric company as of 2004. To our
(EIA 2001).18                                    knowledge, neither DaimlerChrysler

nor other automakers (besides GM and             market share had dipped to 60% by
                          Ford) have publicly reported estimates           model year 2004, the Big Three still
                          of GHG emissions from their vehicles             accounted for more than 70% of the
                          in use. Vehicles of the Big Three taken          vehicle stock. This lag reflects the
                          together accounted for nearly three              lifetime usage and slow turnover of
                          quarters (73%) of U.S. light vehicle             cars and light trucks, and also implies
                          carbon emissions in 2004.                        a similar persistence of rolling carbon
                             Toyota, Honda and Nissan have                 impacts. According to Davis and Diegel
                          the fourth, fifth and sixth largest shares       (2004), the expected median lifetime
                          of the stock respectively. Since their           for a 1990 model year (MY ) car is
                          fuel economy levels are higher than              16.9 years, while that for a MY1990
                          average, these three firms have rolling          light truck is 15.5 years,20 and lifetimes
                          stock carbon shares (8.6%, 5.5% and              have been continuing to lengthen. It
                          4.6% respectively) that are lower than           should be noted, however, that light
                          their shares of the on-road vehicle pop-         vehicle lifetimes are still shorter than
                          ulation. Other players in the U.S.               those of many other energy-consuming
                          market, including Volkswagen, Mitsu-             items; freight trucks and aircraft last
                          bishi, Hyundai, BMW and Subaru,                  longer than cars, and buildings last
                          each accounted for about 1%–2% stock             much longer (although appliances and
                          share. Kia, though it still has a small          equipment may not).
                          market share, is an example of another
                          company where mix differences lead
                          to a stock carbon share slightly greater         Rolling stock carbon burdens by
                          than the population share of their               market segment
                          vehicles (see Table 1), even though              Another way to examine carbon
                          their fleet has been more fuel efficient         emissions is by major market segment
                          than average.                                    (vehicle class): small cars, midsize cars,
                             Another interesting note: Even                large cars, pickups, vans and SUVs.21
                          though the market share of the Big               Table 2 shows the stock share, carbon
                          Three has been generally declining since         emissions and average fuel efficiency
                          the mid 1970s, and their combined                of these six vehicle segments. This

Light vehicle stock, fuel consumption, and carbon emissions by vehicle class, 2004
                      ROLLING STOCK AS OF 2004 (ALL VEHICLES NEW AND USED)                 MY2004 (NEW FLEET ONLY)

                 Vehicle     On-road        Fuel     Carbon    Vehicle    Carbon     On-road                   Carbon
                population fuel economy consumption emissions population emissions fuel economy Market         burden
Vehicle class   (millions)     (mpg)       (Mbd)     (MMTc)     share      share       (mpg)    share           share
Small cars         65.1         24.3         2.10        77.2     32.0%           25%       24.6        23%      18%
Midsize cars       38.5         21.4         1.46        53.7     18.9%           17%       23.2        17%      17%
Large cars         17.6         19.7         0.72        26.5      8.6%            8%       20.8         7%       8%
Pickups            32.2         16.3         1.63        59.9     15.8%           19%       15.6        16%      15%
Vans               17.3         17.9         0.80        29.5      8.5%            9%       19.1         5%       7%
SUVs               33.1         16.3         1.83        67.5     16.2%           21%       16.9        31%      34%
Cars              121.2         22.6         4.27       157.3     59.5%           50%       23.4        47%      43%
Light trucks       82.5         16.6         4.26       156.9     40.5%           50%       16.7        53%      57%
Overall           203.7         19.6         8.53       314.2    100.0%         100%        19.3       100%     100%

Stock vs. new fleet carbon burden shares by vehicle class, 2004

   Small cars



  Midsize cars

                                                                  On-road stock
         Vans                                                     New fleet

    Large cars

                 0%            10%                 20%              30%             40%
                                         Carbon burden share

breakdown of carbon emissions share by            sions, putting them in fourth place in
vehicle class is also depicted in Figure 4.       terms of carbon share.
   Despite falling sales since 1987,                  SUVs and pickups comprised the
small cars remained the largest segment           third and fourth largest segments, with
of the on-road stock. The 65 million              16.2% and 15.8% of the in-use vehicle
small cars (including small wagons) in            population respectively. However, SUVs
use accounted for 32% of the total U.S.           and pickups were in second and third
light duty vehicle stock in 2004, in              place, respectively, in terms of carbon
contrast to their 23% share of new                emissions in 2004. Each of these two
vehicle sales. Small cars still accounted         segments contributed about one-fifth
for the largest share of rolling stock            of total rolling stock emissions. SUV
carbon emissions, emitting 77 MMTc                carbon emissions in 2004 amounted to
in 2004, or about one-fourth of total             67 MMTc and pickup trucks emitted
light vehicle carbon emissions. The               60 MMTc. The disproportionate share
segment’s 25% carbon share is sub-                of SUV and pickup emissions results
stantially less than its 32% stock share          from their below-par fuel economy,
because of its higher than average fuel           averaging 16.3 mpg for both segments.
economy. U.S. small cars averaged 24.3            This fuel economy level is 17% lower
mpg on-road in 2004, 24% better than              than the stock average and corresponds
the overall average, for an average emis-         to an average emissions rate of about
sions rate of 4.3 tons CO2-equivalent             6.5 tons of CO2-equivalent per year.
per year.22                                       The 67 MMTc emitted by all the SUVs
   Midsize cars were the second largest           on the road in 2004 is comparable to
segment of vehicle population, com-               the carbon emissions from 55 large coal-
prising 19% of the 2004 light vehicle             fired power plants.23
stock. Averaging 21.4 mpg on the road,                The remaining segments, vans
midsize cars accounted for 54 MMTc,               (mainly minivans) and large cars,
or 17% of rolling stock carbon emis-              accounted for smaller portions of the

stock and contributed 9% and 8% of              vehicles that each contribute to more
                      2004 stock carbon emissions                     than 5% of stock carbon emissions
                      respectively. Overall, the 2004 vehicle         include four segments of General
                      stock composition was 59% cars and              Motor’s products (small cars, midsize
                      41% light trucks. But the rolling carbon        cars, pickups, SUVs) and two segments
                      shares were roughly 50% each for cars           of Ford’s products (pickups and SUVs).
                      and light trucks, reflecting the higher         GM’s and Ford’s pickups are the two
                      CO2 emissions rates of trucks compared          groups with the largest emissions over-
                      to cars.                                        all, accounting for 6.8% and 6.6% of
                         Tables 3 and 4 cross-tabulate stock          carbon share, respectively. Since our data
                      share and carbon share, respectively, by        exclude Class 2b trucks (8,501–10,000
                      segment and automaker. Groups of                lb GVW), which are mostly three-

Vehicle population cross-tabulation by automaker and vehicle class, 2004
Manufacturer      Small cars     Midsize cars     Large cars          Pickups      Vans      SUVs       Overall
GM                   8.2%            6.9%             4.4%             5.6%       2.1%       4.4%        31.6%
Ford                 6.3%            4.0%             2.7%             5.6%       2.1%       3.8%        24.4%
DaimlerChrysler      2.9%            2.0%             1.2%             2.2%       3.2%       3.5%        14.9%
Toyota               3.2%            2.2%             0.4%             1.5%       0.4%       1.5%         9.1%
Honda                3.9%            1.5%                                         0.4%       0.8%         6.5%
Nissan               2.1%            1.1%                              0.8%       0.2%       0.7%         4.9%
Volkswagen           1.4%            0.4%
quarter- and one-ton pickups, the actual               from the Big Three’s automobiles in
carbon emissions share of pickups over-                2004 were comparable to the total from
all is greater still.24                                the top 11 electric companies. Next
                                                       down the list, the CO2 emissions from
                                                       Toyota vehicles were slightly higher
Comparing automobile and                               than those from the Tennessee Valley
electric sector carbon emissions                       Authority, the nation’s third largest
Accounting for roughly 20% of U.S.                     power producer.
energy-related CO2 emissions, cars and                    Comparing CO2 emissions from on-
light trucks are a key source of the                   road stocks (rather than just new sales)
nation’s global warming emissions.                     to those from electric utilities is appro-
Viewed in a corporate impact context,                  priate in that both include the emissions
GM, Ford and DaimlerChrysler                           of long-lived products and equipment
vehicles are the first, second and third               (automobiles and appliances or other
largest CO2 emitters in the United                     electrical devices). Both are influenced
States, all ahead of country’s largest                 by the actions of end-users, that is,
electricity producer, American Electric                consumers and businesses. For example,
Power (AEP). Such comparisons are                      a power company’s CO2 emissions are
illustrated in Figure 5.                               the result of the electricity consumed in
    The 99 MMTc from GM vehicles                       homes, offices, schools and other power-
in 2004 was more than double the                       using facilities in its service area. Both
41 MMTc from AEP. Ford’s cars and                      are influenced by the carbon intensity of
trucks emitted 80 MMTc, essentially                    their fuel supply. For example, coal
double AEP’s emissions that year, and                  accounts for 54% of energy consumed
DaimlerChrysler’s products emitted                     by U.S. power generation25 and 83% of
51 MMTc. The total CO2 emissions                       carbon emissions from the electric

Carbon emissions of major automakers’ products vs. major electric
producers in the United States, 2004

             General Motors                                                          99
                         Ford                                              80
            DaimlerChrysler                                   51
     American Electric Power                             41
         Southern Company                              37
                       Toyota                    27
   Tennessee Valley Authority                    26
                                                              Major automakers’ products
                       Honda                17                Major electric producers
                         Xcel               17
                     Ameren                 17
                     Cinergy               16
                   Dominion                15
        Edison International               15
            Progress Energy                15
                      Nissan               15
                                   0       20         40           60     80       100      120
                                                      Carbon emissions (MMTc)

Source: Table 1 and CERES et al. (2006).

sector.26 Government decisions and                ways, particularly in the nature of the
policies are also important in both cases.        markets and the specific roles played by
State and local regulators oversee elec-          the other actors who influence usage.
tric utility services and rates for the              Another way to view corporate CO2
power sector, and multiple levels of              emissions impacts would be to tally
government oversee transportation                 those associated with the motor fuel
infrastructure, finance and land use              sales by major oil companies, but we
planning for automobiles. The sectors             have not attempted such an analysis
are, of course, different in many other           due to lack of data.27

Beyond the carbon tally

             The rolling stock snapshot for 2004 is            quantifiable and can be tracked through
             the product of many forces. Key factors           time, and examining them forms a
             include the amount of travel, the level of        common basis for analyzing the car-
             fuel economy and the carbon content of            climate problem.
             motor fuel. Among these factors, only                For the 2004 rolling carbon snapshot
             fuel economy has served to partially              discussed in this report, total U.S. auto
             control CO2 emissions. Fuel carbon                sector CO2 emissions can be viewed as
             intensity has not significantly changed,          the product of:
             reflecting the tenacity of oil as a source
             of motor fuel and the fact that no sys-           • Travel demand (2.6 × 1012 miles/year)
             tematic effort has been made to reduce            • Fuel use rate (51 gallons/1000 miles)
             or offset GHG emissions associated                • Fuel carbon content (5.3 pounds of
             with petroleum fuels. Many forces drive             carbon/gallon)
             travel demand, and all of them have had
             a combined effect of pushing auto sector          The result rounds out to the 314 MMTc
             CO2 emissions upward.                             total of rolling stock carbon emissions
                                                               given in Tables 1 and 2.
                                                                  The first factor, known as vehicle
             Factors determining auto sector                   miles traveled (VMT), represents the
             CO2 emissions                                     total amount of driving in cars and light
             As illustrated in Figure 6, auto sector           trucks.28 The second factor, average
             CO2 emissions can be depicted as a                fuel use per mile, is based on the stock
             three-legged stool, with the overall level        average fuel economy of 19.6 mpg.
             propped up by the three major factors             The third factor, fuel carbon content
             noted. These factors are generally                of 5.3 pounds/gallon, represents the
                                                               carbon in gasoline.29
                                                                  A look at what’s behind each of the
             FIGURE 6                                          three legs of the car-carbon stool sheds
             Three main factors behind rolling
                                                               light on the multifaceted nature of auto
                                                               sector carbon emissions and puts into
                                                               perspective the challenge of addressing
                     Vehicle CO2 emissions                     a problem of this magnitude.

                                                               TRAVEL DEMAND
                                                               Demographic and economic factors,
                                                               urban and regional development, changes
                                                               in transportation infrastructure and
                                                               evolving land-use patterns all influence
                                                               the amount of driving. The travel demand
                                                               factor, however, is often given but passing
                                                               attention in U.S. climate policy, and dis-
                                                               cussions frequently focus on the politically
               Travel                          Fuel            charged issue of raising fuel taxes.
              demand        Fuel use rate     carbon              In the United States, road building,
                                                               automaking and the supply of petroleum

fuels form a three-way symbiosis that                         pounding population growth are
has served to sustain steady increases in                     increases in vehicle ownership rates and
driving. The public appreciates the                           average VMT per capita, as shown in
benefits of automobiles enough to                             Figure 7. Both have grown steadily over
support fuel taxes that help pay for                          the second half of the 20th century.
roads. Yet taxes receive great scrutiny,                      VMT per capita has increased 82%
and taxes on fuel generally have been                         since 1970—double the population
limited to the minimum needed to cover                        growth over this period—rising from
basic highway costs.                                          roughly 5,400 miles per year to 9,900 by
   The personal value of the car is high                      2002. Car ownership (vehicles per
enough that this major part of the trans-                     capita) has risen essentially in parallel.
portation system is privately financed                        Figure 7 shows ownership over the
by consumers themselves. Even during                          entire population, including children,
price spikes, fuel cost is generally a small                  the very old and others who do not
fraction of the total cost of owning and                      drive. The intensity of auto use is
operating a car.30 Thus, U.S. fuel prices                     highlighted by the fact that there are
provide little restraint on VMT. Absent                       now more cars than drivers, with the
effective policies to manage transporta-                      latest statistics showing that the United
tion demand at the national scale, VMT                        States has 1.06 personal vehicles per
has increased steadily for many years.                        licensed driver.33
Net VMT growth was 158% between                                  Surveys of how Americans use their
1970 and 2004, for an average growth                          cars are commonly reported on a house-
rate of 2.8% per year.31                                      hold basis, as shown in Figure 8. The
   A key factor driving travel demand is                      average household drove roughly
population. The U.S. population in 2002                       21,000 miles in 2001, 17% more than
was 288 million, representing an                              the household average in 1990. While
increase of 41% since 1970, and an                            commuting trips still had the largest
increase of 90% since 1950.32 Com-                            share of driving, American households

U.S. vehicle ownership and VMT per capita (1950–2002)

                         0.9                                                                12,000

                                   Vehicles per capita                                      10,000
                                   VMT per capita
                                                                                                     VMT per capita (miles)
   Vehicles per capita

                         0.6                                                                 8,000


                         0.3                                                                 4,000


                         0.0                                                                    0
                            1950   1960           1970        1980       1990        2000

Source: Davis and Diegel (2004), Table 8.2

VMT trend by travel purpose


                               I Other
                               I Social and recreation
                    20,000     I Misc. family and personal business
                               I Shopping
                               I To and from work

   Miles per year



                        1969          1977          1983              1990    1990a*       1995           2001
                                                             Year of survey

Source: Hu and Reuscher (2004), Table 6.
*The survey methodology changed in 1995 and so the 1990 results are shown in two forms: using original survey
 definitions (labeled "1990") and adjusted for comparison to the 1995 and 2001 surveys (labeled "1990a").

are using their vehicles more often                                reductions have not been enough to
for shopping. The number of miles                                  achieve healthy air in many regions
for shopping trips steadily increased                              (Scott et al. 2005). Thus, in addition
since 1969, and grew by 40% from                                   to ongoing efforts to improve tech-
1990 to 2001, as a result of increased                             nology, renewed attention is being
shopping trips and extended trip                                   placed on improved land use, trans-
lengths.34 These statistics highlight the                          portation alternatives and rationalized
trend of Americans’ increasing reliance                            pricing to achieve a more efficient
on personal vehicles, a natural conse-                             transportation system that is less reliant
quence of burgeoning auto-oriented                                 on motor vehicles.
development that has been the norm
in most parts of the United States over                            FUEL ECONOMY
the past several decades.                                          The 1970s oil crises—with gasoline
   The issue of how to manage travel                               lines, fears of shortages and suddenly
demand, which is intimately linked to                              higher fuel prices, plus the policy
land use and many other factors, is quite                          response of Corporate Average Fuel
involved. However, a growing sense of                              Economy (CAFE) standards—drove a
the limitations of traditional transporta-                         leap in new light vehicle fuel economy
tion priorities reveals many reasons                               between 1975 and 1981. Fuel economy
to pursue policies that would serve to                             continued to slowly increase between
dampen VMT growth (TRB 2005).                                      1981 and 1988 but then began declining
As noted in the next section, catalytic                            due to the rising popularity of light
converters have succeeded in cutting                               trucks and largely unchanged CAFE
air pollution in spite of VMT growth;                              standards. Nevertheless, the EPA-rated
nevertheless, such technology-based                                fuel economy of the new automobile

fleet saw a net 78% increase from                                 health-harming pollution from cars and
1974–2004. Adjusting for increased                                light trucks.36 This drop in total emis-
shortfall, average on-road fuel economy                           sions was achieved by cutting stock-
improved by roughly 50% over that                                 average per-mile emission rates to
period.35 This efficiency gain implies a                          roughly 15% of their pre-control levels.
33% reduction in CO2 emissions per                                In short, catalyst-based emissions
mile from today’s vehicles compared to                            control—incorporating computerized
those of a generation ago.                                        engine management, reformulated low-
   It is instructive to compare the fuel-                         sulfur gasoline and related devices—has
economy driven reductions in CO2                                  been a potent enough technological fix
emissions with the reductions in the                              to achieve net pollution reductions in
emissions of other forms of vehicle                               spite of increased driving.
pollution. Efforts to seriously control                              The difference between the effective-
smog-forming automobile emissions                                 ness of tailpipe emissions controls and
also began in the 1970s. The Clean Air                            fuel economy improvement over this
Act limited tailpipe emissions of                                 period is illustrated in Figure 9. The
hydrocarbons (HC), nitrogen oxides                                backdrop for both air pollution and CO2
(NOx) and carbon monoxide (CO) by                                 emissions from cars and light trucks is
model year 1975 to levels that most                               VMT growth, which, as described
vehicles could attain only through the                            earlier, rose by more than a factor of
use of catalytic converters (Mondt                                2.5 since 1970. Yet total health-damaging
2000). Today, after an ongoing                                    air pollution from U.S. automobiles
tightening of tailpipe standards and a                            dropped by nearly 10 million tons of
generation of effort, the United States                           NOx-equivalent,37 corresponding to
has achieved over a 60% reduction in                              the 60% reduction noted. Reductions
automotive “rolling smog,” that is,                               will continue as even tighter tailpipe

Trends in carbon dioxide emissions and other air pollution from U.S.


                      1.8           Carbon dioxide
                                    Other air pollutants                 Up by 70% (+114 million tons)

   Index (1970 = 1)





                                                                             Down by 63% (–10 million tons)
                            1970   1975       1980         1985       1990        1995          2000         2005

Source: Authors’ analysis of EPA (2005b), FHWA (2006) and historical editions of Highway Statistics. The “other air
pollutants” trend is based on a health-damage-weighted composite for tailpipe emissions of nitrogen oxides (NOx),
volatile organic compounds (VOC), particulates (PM10), carbon monoxide (CO) and sulfur dioxide (SO2).

standards are phased in. Automotive                However, by the mid-1990s it became
CO2 emissions, on the other hand, have             clear that all standards short of the zero-
increased by 70% since 1970 and are                emission vehicle (ZEV) mandate could
continuing to rise. Although many tech-            be met with improved catalytic controls
nologies are available to cut CO2 emis-            and reformulated gasoline.
sions rates, none of the options (not even            Most alternative fuels are now pro-
hybrid powertrains) are as effective as the        moted as offering low GHG emissions.
catalytic converter has been for cutting           An ongoing debate plays out in numer-
conventional pollutants. Lacking such a            ous paper studies (“full fuel cycle”
technological fix, vehicle design changes          analyses) of which fuels might have low
will need to be complemented by other              or zero GHG emissions under various
strategies, such as low-carbon fuels and           assumptions. However, requirements to
reductions in travel demand, to see major          control GHG emissions throughout a
progress in reducing rolling carbon.               fuel’s life cycle are yet to be developed.
                                                   Since little work has been done to
LOW-CARBON FUELS                                   systematically measure and track the
The 1970s energy crisis also prompted              actual fuel-cycle impacts of commer-
efforts to develop and commercialize               cially produced fuels, the real-world
alternatives to petroleum-based trans-             greenhouse gas implications of alter-
portation fuels. Since then, the U.S.              native fuels remain uncertain. Moreover,
economy has seen major shifts in the               one major U.S. policy to promote alter-
structure of oil use; sectors that could           native fuels, giving automakers CAFE
switch to other fuels have largely done            credits for selling flexible-fuel vehicles
so. Non-transportation oil use is now              (FFVs), is counterproductive. The
lower in absolute terms than it was in             resulting trade-off in vehicle efficiency
1970, even after three decades of eco-             has increased oil consumption and
nomic growth. Transportation, however,             carbon emissions over what they would
remains 96% petroleum dependent, and               have been without the FFV policy
the sector now accounts for two-thirds             (DOT 2002).
of U.S. oil use, compared to one-half                 One alternative fuel that has seen
in 1970.38                                         consistent backing is ethanol. Ethanol
   Throughout this time a variety of               can be readily blended with gasoline in
fuels have been promoted by federal                low concentrations and such “gasohol”
and state policies. Alternatives that have         has long been available in the Midwest.
seen support include synthetic fuels               U.S. fuel ethanol use is now increasing
(synfuels) from coal and oil shales,               rapidly toward the renewable fuel man-
natural gas, methanol (derived from                date of 7.5 billion gallons by 2012.40
natural gas or coal), various biofuels,            That level would amount to about 3% of
electricity and hydrogen.39                        U.S. light vehicle fuel consumption.41
   Although nearly all alternative fuels           However, because the energy use and
are advertised as “clean,” policies to             emissions associated with agricultural
promote them have had few if any                   and ethanol production processes are
stipulations regarding environmental               not tracked, it is difficult to ascertain
performance beyond those already                   the net carbon impact of ethanol use.
required for gasoline. California’s 1990           A recent meta-study found that replac-
low-emission vehicle (LEV) program                 ing gasoline with corn ethanol has an
was partly premised on levels of strin-            ambiguous effect on GHG emissions
gency that would favor alternative fuels.          (Farrell et al. 2006). Like most commercial

and agricultural activity in the United             suppliers and consumers, as well as by
States, ethanol production is now pur-              regional planning bodies and other
sued without a need to manage carbon.               transportation policy forums.
To ensure reductions in GHG emissions                  For example, consider fuel economy,
through fuel substitution, protocols will           a tangible and easy-to-track factor
need to be established for tracking fuel-           behind automotive CO2 emissions.42
cycle impacts and certifying that the net           Consumers influence fuel economy
GHG emissions from ethanol or other                 through their selection of vehicles as
fuels are measurably lower than those               well as their driving and maintenance
from gasoline.                                      habits. Automakers influence fuel
   Fuel supply infrastructure is long-              economy through their product strategies
lived, with large-scale investments                 and design choices. But the decisions
needed to develop new fuel production               made by consumers and automakers
facilities, so shifting to alternative fuels        are not independent; moreover, the net
requires longer lead times than modi-               carbon impact of fuel economy depends
fying vehicles. Although the past few               on the broader influences that shape
years have seen high oil prices, and the            vehicle use.
U.S. Department of Energy revised its
oil price outlook significantly upward              RECASTING THE DISCUSSION
(EIA 2005), the competitive environ-                The complex, market- and policy-
ment for petroleum alternatives remains             mediated nature of decisions that
speculative. This uncertainty in com-               influence CO2 emissions is not unique
mercial outlook compounds the uncer-                to the auto sector, of course. But our
tainty in the carbon impacts of any given           rolling stock tally underscores the mag-
fuel due to the lack of policies for man-           nitude of automotive CO2 emissions
aging GHG emissions associated with                 and spotlights the roles of the many
fuel production. Therefore, while shift-            actors whose decisions are behind the
ing to low-carbon fuels is an essential             314 MMTc from U.S. cars and light
complement to cutting travel demand                 trucks. Such a view suggests a need to
and raising fuel economy, how well new              recast the discussion of what to do about
fuels will serve to reduce GHG emis-                the car-carbon problem from
sions depends on programs and policies
that largely remain to be developed.                What policies are needed to address
                                                    each factor behind automotive CO2
Managing auto sector carbon
While the major factors that determine              to
emissions—the three-legged stool of
travel demand, fuel economy and type of             What policies can motivate each actor
fuel—provide a convenient snapshot of               to address the aspects of CO2 emissions
the sector, such an analysis has limitations        under each actor’s control?
when considering how to cut emissions.
Multiple decision makers (“actors”) in-                In a market-based framework, only
fluence each leg of the stool. In other             individual decision makers can deter-
words, the factors that technically deter-          mine the actual, perceived costs and
mine emissions are the product of                   benefits to themselves resulting from
choices made by many players in the                 the decisions they make. Developing
marketplace, such as automakers, fuel               an actor-based carbon management

framework can clarify the roles of all             regional governments as well as state
players and enable cost-effective deci-            officials to explicitly manage carbon
sions about carbon reduction. Under                impacts in all aspects of transportation
this framework, policies can be designed           and land use planning. Such decisions
to motivate actors to consider and                 are the clear area in which local govern-
reduce carbon impacts of every decision            ments can affect the “rolling carbon”
they can control. Such an approach                 impacts of their jurisdiction. Challenges
would be a step beyond factor-based                and costs are likely be associated with
analysis, which rests on assumptions               any of the actions a city might consider
about the costs and benefits to particular         for cutting carbon from transportation,
actors presumed to hold the most influ-            but there might also be cost savings.
ence over a given factor.                             A city is just one actor, but the above
                                                   example illustrates how any entity in-
A NEED FOR NEW TOOLS                               fluencing auto sector CO2 emissions can
Exactly how to define a set of auto-               approach the problem under a carbon
sector specific carbon management                  management paradigm. A private com-
policies is a subject for future work. We          pany or institution that uses vehicles in
can, however, illustrate the value of such         the course of business also has a measure
an approach by considering the example             of control over the associated CO2 emis-
of a city as an actor who can influence            sions, and opportunities to reduce emis-
the CO2 emissions associated with its              sions can be found once an effort is
transportation operations. The vehicles            made to look for them. Right now,
a city operates are, in fact, a microcosm          however, most cities (as well as most
of the larger rolling carbon situation.            other entities who influence auto sector
   To cut the carbon from a city’s                 CO2 emissions) have little way of know-
transportation operations, its agencies            ing how their day-to-day or year-by-
might consider ways to carry out their             year transportation decisions impact
functions with less driving; they might            CO2 emissions. Thus, a starting point
change the number, type and efficiency             for finding ways to cut emissions is
of the vehicles they operate; or they              developing new evaluation tools that
might use low-carbon fuels.43 Changes              make the carbon impacts and costs of
in vehicle purchases would influence the           decision options explicit. Sector-specific
demand side of the market to which                 carbon impact evaluation tools will
automakers respond. Moreover, under                facilitate “carbon-sensitive decision
such a fleet carbon management ap-                 making,” enabling each actor to make
proach, decisions about vehicle choice             the decisions that most affordably
would no longer be made in isolation               reduce their portion of emissions. A
from looking at other (and sometimes               broader question is how to motivate
more accessible) ways for the city to cut          carbon-sensitive decision-making. Ulti-
carbon from its vehicles.                          mately, those who reduce emissions
   Of course, a municipality’s vehicle             might be able to realize a financial value
fleet is just a small fraction of all the          from their actions in the market for car-
vehicles within a community. In fact,              bon reductions that will emerge under
beyond its own fleet, city officials have a        national and international climate
measure of control over land-use, zoning           protection regimes.
and development decisions, parking and                In short, many different entities have
the availability of non-auto modes of              some measure of control over auto sector
transportation. A city can help lead other         CO2 emissions. Opportunities to cut

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