US road transport by Greenhouse Gas Protocol


Road vehicle emissions methodology. Calculates direct fossil and/or biogenic carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and carbon dioxide equivalent (CO2e) emissions associated with distance travelled or fuel consumed. Choices include vehicle type, fuel type and emissions standard. United States.


This methodology represents greenhouse gas emissions associated with the road transport in the US. The data and calculation methodology is based on those provided in the Greenhouse Gas Protocol worksheet GHG emissions from transport or mobile sources (version 2.2), published in June 2011.

The methodology

Emissions model

The emissions methodology is based upon emissions factors which describe the rate at which greenhouse gas emissions are produced during road-based travel.

As with other leading greenhouse gas data and calculation methodology sources (e.g. IPCC, EPA), this methodology assumes that CO2 emissions are directly related to the quantity of carbon which is oxidised during combustion and therefore directly proportional to the quantity of fuel consumed, whereas emissions of CH4 and N2O are more closely related to other factors, including distance travelled.

Therefore, in the best case scenario - where both fuel consumption and distance travelled can be specified - CO2 emissions are calculated on the basis of fuel consumption and CH4 and N2O emissions on the basis of distance travelled. In those cases where only one of fuel consumption and distance travelled can be specified, however, the Greenhouse Gas Protocol methodology converts the original (EPA) emissions factors into the required basis (distance, fuel volume) using 'typical' fuel efficiency data for the vehicles types represented. As such, calculations of CO2, CH4 and N2O can be made on the basis of either fuel consumed, distance travelled or - ideally - both.

Since the CO2 produced during the burning of biofuels in not a net contributor to atmospheric warming (see here), fossil- and biofuel-associated CO2 are explicitly defined.

All emissions factors represent emissions associated with entire vehicles (e.g. car, motorcycle), which can be contrasted with similar transport-related emissions factors which describe emissions on the basis of individual passengers. Emissions for individual passengers can nevertheless be derived by 'sharing' vehicular emissions across all vehicle occupants, if the occupancy of the vehicle is known.

Emissions - expressed in terms of mass (e.g. kg) - are calculated by multiplying these rates (mass emitted per distance or volume [fuel]; e.g. kg CO2 per mile or gallon) by a distance (e.g km) travelled or fuel (e.g. gallon) consumed.

Model data

The rate at which road transportation produces greenhouse gas emissions varies with the type of vehicle, depending on factors such as the type of fuel used (e.g. gasoline/petrol, diesel), and emissions control standards. Therefore, emissions factors for a broad range of generalised US road transport scenarios are provided.

A total of 75 specific types of road transport are represented and are differentiated by vehicle type (i.e. bus, car, light and heavy goods vehicles, motorcycles), fuel type (gasoline/petrol, diesel, ethanol, LPG, LNG) and emissions standard. For each vehicle represented, specific emissions factors are used to calculate greenhouse gas emissions according to the activity data provided. In total, the following emissions factors are provided for each vehicle type:

  • Fossil CO2 emissions per unit distance travelled
  • Biogenic CO2 emissions per unit distance travelled
  • CH4 emissions per unit distance travelled
  • N2O emissions per unit distance travelled
  • CH4 emissions per unit fuel consumed
  • N2O emissions per unit fuel consumed
CO2 emissions per unit fuel consumed are referenced from this related Greenhouse Gas Protocol methodology. Both fossil- and biogenic-CO2 emissions factors are provided although the latter is applicable only to ethanol.

Activity data required

According to this methodology, greenhouse gas emissions can be calculated on the basis of fuel consumed, distance travelled or - for most accurate results - both. Therefore either or both of these values must be specified in order to make an emissions calculation.

If multiple passengers are under consideration, this number can be specified, in which case vehicle emissions are shared amongst all passengers.

Calculation and result

The returned quantities for this methodology represent CO2, biogenic CO2, CH4, N2O and CO2e emissions associated with the activity data (distance/fuel) specified. In most cases CO2 emissions are entirely represented by fossil CO2 as only biofuels (in this case, ethanol) or biofuel blends contain biogenic carbon. CO2e emissions represent all three gases (fossil CO2 only), converted using these global warming potential)

Similar methodologies

Other Greenhouse Gas Protocol transport methodologies are available representing general transport fuel consumption, fuels consumed in specific transport contexts, freight transport, passenger/public transport, road transportation in the UK (with heavy goods) and other regions.

01RQ49NQU22I bus, diesel
35WBT4B407YP bus, ethanol
0QJHX5XPWTMK bus, gasoline
MJ6KRLQIJN65 heavy duty vehicle (articulated), diesel, 1960-present
PHTJ27I7UI2B heavy duty vehicle (articulated), ethanol
GIBI1WU08TUL heavy duty vehicle (articulated), gasoline, 1985-1986
0L1XOUD8B5D7 heavy duty vehicle (articulated), gasoline, 1987
0GWAZ84SP0AQ heavy duty vehicle (articulated), gasoline, 1988-1989
14V3KQ69CRG4 heavy duty vehicle (articulated), gasoline, 1990-1995
R19MVMSHJF34 heavy duty vehicle (articulated), gasoline, 1996
CA7WKZJO7JSA heavy duty vehicle (articulated), gasoline, 1997
LO6NATYUABU1 heavy duty vehicle (articulated), gasoline, 1998
4L9YR370A3UC heavy duty vehicle (articulated), gasoline, 1999
G63ACK3HF9P0 heavy duty vehicle (articulated), gasoline, 2000
Y0N3DU5GSNPY heavy duty vehicle (articulated), gasoline, 2001
1AS9T8UP1EJP heavy duty vehicle (articulated), gasoline, 2002
LT4KSF7RBPJR heavy duty vehicle (articulated), gasoline, 2003
GSBP31WZ8UIL heavy duty vehicle (articulated), gasoline, 2004
TQKNU7WHTL5X heavy duty vehicle (articulated), gasoline, 2005-present
A9Y63YZCZKXP heavy duty vehicle (articulated), lng
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