Domestic transportation CO2 emissions increased by 21 percent (315.4 MMT CO2) between 1990 and 2016, an annualized increase of 0.8 percent. Among domestic transportation sources in 2016, light-duty vehicles (including passenger cars and light-duty trucks) represented 59 percent of CO2 emissions from fossil fuel combustion, medium- and heavy-duty trucks and buses 24 percent, commercial aircraft 7 percent, and other sources 9 percent. See Table 3-12 for a detailed breakdown of transportation CO2 emissions by mode and fuel type.
Almost all of the energy consumed by the transportation sector is petroleum-based, including motor gasoline, diesel fuel, jet fuel, and residual oil. Carbon dioxide emissions from the combustion of ethanol and biodiesel for
transportation purposes, along with the emissions associated with the agricultural and industrial processes involved in the production of biofuel, are captured in other Inventory sectors.23Ethanol consumption from the transportation sector has increased from 0.7 billion gallons in 1990 to 13.5 billion gallons in 2016, while biodiesel consumption has increased from 0.01 billion gallons in 2001 to 2.1 billion gallons in 2016. For further information, see Section 3.11 on biofuel consumption at the end of this chapter and Table A-96 in Annex 3.2.
Carbon dioxide emissions from passenger cars and light-duty trucks totaled 1,058.5 MMT CO2 in 2016. This is an increase of 14 percent (133.6 MMT CO2) from 1990 due, in large part, to increased demand for travel as fleet-wide light-duty vehicle fuel economy was relatively stable (average new vehicle fuel economy declined slowly from 1990 through 2004 and then increased more rapidly from 2005 through 2016). Carbon dioxide emissions from passenger cars and light-duty trucks peaked at 1,150.6 MMT CO2 in 2004, and since then have declined about 8 percent. The decline in new light-duty vehicle fuel economy between 1990 and 2004 (Figure 3-13) reflected the increasing market share of light-duty trucks, which grew from about 30 percent of new vehicle sales in 1990 to 48 percent in
23 Biofuel estimates are presented in the Energy chapter for informational purposes only, in line with IPCC methodological guidance and UNFCCC reporting obligations. Net carbon fluxes from changes in biogenic carbon reservoirs in croplands are accounted for in the estimates for Land Use, Land-Use Change, and Forestry (see Chapter 6). More information and additional analyses on biofuels are available at EPA's Renewable Fuels Standards website. See <https://www.epa.gov/renewable-fuel-standard-program>.
2004. Starting in 2005, average new vehicle fuel economy began to increase while light-duty VMT grew only modestly for much of the period. Light-duty VMT grew by less than one percent or declined each year between 2005 and 201324 and has since grown at a faster rate (2.6 percent from 2014 to 2015, and 2.5 percent from 2015 to 2016). Average new vehicle fuel economy has increased almost every year since 2005, while the light-duty truck share decreased to about 33 percent in 2009 and has since varied from year to year between 36 and 43 percent.
Light-duty truck share is about 38 percent of new vehicles in model year 2016 (EPA 2016a). See also Annex 3.2 for data by vehicle mode and information on VMT and the share of new vehicles (in VMT).
Medium- and heavy-duty truck CO2 emissions increased by 82 percent from 1990 to 2016. This increase was largely due to a substantial growth in medium- and heavy-duty truck VMT, which increased by 100 percent between 1990 and 2016.25 Carbon dioxide from the domestic operation of commercial aircraft increased by 10 percent (10.5 MMT CO2) from 1990 to 2016.26 Across all categories of aviation, excluding international bunkers, CO2 emissions decreased by 11 percent (19.9 MMT CO2) between 1990 and 2016.27 This includes a 66 percent (22.7 MMT CO2) decrease in CO2 emissions from domestic military operations.
Transportation sources also produce CH4 and N2O; these emissions are included in Table 3-13 and Table 3-14 and in the CH4 and N2O from Mobile Combustion section. Annex 3.2 presents total emissions from all transportation and mobile sources, including CO2, CH4, N2O, and HFCs.
24VMT estimates are based on data from FHWA Highway Statistics Table VM-1 (FHWA 1996 through 2017). In 2007 and 2008 light-duty VMT decreased 3.0 percent and 2.3 percent, respectively. Note that the decline in light-duty VMT from 2006 to 2007 is due at least in part to a change in FHWA's methods for estimating VMT. In 2011, FHWA changed its methods for estimating VMT by vehicle class, which led to a shift in VMT and emissions among on-road vehicle classes in the 2007 to 2016 time period. In absence of these method changes, light-duty VMT growth between 2006 and 2007 would likely have been higher.
25 While FHWA data shows consistent growth in medium- and heavy-duty truck VMT over the 1990 to 2016 time period, part of the growth reflects a method change for estimating VMT starting in 2007. This change in methodology in FHWA’s VM-1 table resulted in large changes in VMT by vehicle class, thus leading to a shift in VMT and emissions among on-road vehicle classes in the 2007 to 2016 time period. During the time period prior to the method change (1990 to 2006), VMT for medium- and heavy-duty trucks increased by 51 percent.
26 Commercial aircraft, as modeled in FAA’s AEDT, consists of passenger aircraft, cargo, and other chartered flights.
27 Includes consumption of jet fuel and aviation gasoline. Does not include aircraft bunkers, which are not included in national emission totals, in line with IPCC methodological guidance and UNFCCC reporting obligations.
Figure 3-13: Sales-Weighted Fuel Economy of New Passenger Cars and Light-Duty Trucks, 1990–2016 (miles/gallon)
Source: EPA (2016a)
Figure 3-14: Sales of New Passenger Cars and Light-Duty Trucks, 1990–2016 (Percent)
Source: EPA (2016a)
Table 3-12: CO2 Emissions from Fossil Fuel Combustion in Transportation End-Use Sector
Total (Including Bunkers)f 1,574.1 1,973.6 1,771.6 1,781.4 1,824.6 1,850.1 1,902.7
Biofuels-Ethanoli 4.1 22.4 71.5 73.4 74.9 75.9 78.2
Biofuels-Biodieseli + 0.9 8.5 13.5 13.3 14.1 19.6
+ Does not exceed 0.05 MMT CO2 Eq.
International Bunker Fuels from Commercial Aviation
a In 2011 FHWA changed its methods for estimating vehicle miles traveled (VMT) and related data. These methodological changes included how vehicles are classified, moving from a system based on body-type to one that is based on wheelbase.
These changes were first incorporated for the 1990 through 2010 Inventory and apply to the 2007 through 2016 time period.
This resulted in large changes in VMT and fuel consumption data by vehicle class, thus leading to a shift in emissions among on-road vehicle classes.
b Gasoline and diesel highway vehicle fuel consumption estimates are based on data from FHWA Highway Statistics Table MF-21, MF-27, and VM-1 (FHWA 1996 through 2017). Data from Table VM-1 is used to estimate the share of consumption between each on-road vehicle class. These fuel consumption estimates are combined with estimates of fuel shares by vehicle type from DOE’s TEDB Annex Tables A.1 through A.6 (DOE 1993 through 2016). TEDB data for 2016 has not been published yet, therefore 2015 data are used as a proxy.
c Includes medium- and heavy-duty trucks over 8,500 lbs.
d In 2014, EPA incorporated the NONROAD2008 model into MOVES2014. The current Inventory uses the NONROAD component of MOVES2014a for years 1999 through 2016.
e Note that large year over year fluctuations in emission estimates partially reflect nature of data collection for these sources.
f Official estimates exclude emissions from the combustion of both aviation and marine international bunker fuels; however, estimates including international bunker fuel-related emissions are presented for informational purposes.
g Commercial aircraft, as modeled in FAA’s Aviation Environmental Design Tool (AEDT), consists of passenger aircraft, cargo, and other chartered flights.
h Pipelines reflect CO2 emissions from natural gas-powered pipelines transporting natural gas.
i Ethanol and biodiesel estimates are presented for informational purposes only. See Section 3.11 of this chapter and the estimates in Land Use, Land-Use Change, and Forestry (see Chapter 6), in line with IPCC methodological guidance and UNFCCC reporting obligations, for more information on ethanol and biodiesel.
j Transportation sector natural gas and LPG consumption are based on data from EIA (2017). Prior to the previous (i.e., 1990 through 2015) Inventory, data from DOE TEDB were used to estimate each vehicle class’s share of the total natural gas and LPG consumption. Since TEDB does not include estimates for natural gas use by medium and heavy-duty trucks or LPG use by passenger cars, EIA Alternative Fuel Vehicle Data (Browning 2017) is now used to determine each vehicle class’s share of the total natural gas and LPG consumption. These changes were first incorporated in the previous Inventory and apply to the 1990 to 2016 time period.
k Includes emissions from rail electricity.
Notes: This table does not include emissions from non-transportation mobile sources, such as agricultural equipment and construction/mining equipment; it also does not include emissions associated with electricity consumption by pipelines or lubricants used in transportation. In addition, this table does not include CO2 emissions from U.S. Territories, since these are covered in a separate chapter of the Inventory. Totals may not sum due to independent rounding.