This methodology represents greenhouse gas emissions associated with the passenger transport in the geographic contexts of the US, UK and other regions. 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 emissions methodology is based upon emissions factors which describe the rate at which greenhouse gas emissions are produced during travel in relation to distance travelled. These emissions factors represent emissions associated with individual passengers, which can be contrasted with similar transport-related emissions factors which describe emissions on the basis of entire vehicles (e.g. car, motorcycle).
Emissions - expressed in terms of mass (e.g. kg) - are calculated by multiplying these rates (mass emitted per distance; e.g. kg CO2 per mile) by a distance (e.g mile) travelled.
The rate at which passenger transportation produces greenhouse gas emissions varies with the mode of transport, depending on factors such as the fuel efficiency (i.e. the distance achieved per unit of fuel consumed) of the particular type of vehicle (e.g. lorry, plane, train, ship) as well as the typical passenger loading. Fuel efficiency may be related factors such as the type of fuel used (e.g. petrol, diesel, biofuel, electricity) and the physical dynamics of the transportation context (i.e. road, rail, water, air). The loading of passengers indicates the extent to which the emissions of the entire vehicle can be 'shared' between individual passengers. Therefore, emissions factors for a broad range of generalised passenger transport scenarios are provided.
A total of 57 specific types of passenger transport scenarios are represented and are differentiated by transport type (i.e. air, bus, ferry, rail, taxi), passenger class (in the case of air travel) and region (UK, US, other regions).
Most transport types (bus, rail, taxi) are represented by three distinct emissions factors which differentiate greenhouse gas emissions into CO2, CH4 and N2O. For air and ferry travel, only emissions factors for CO2 are provided as part of this methodology, and therefore only CO2 emissions associated with these forms of transport can be calculated (CH4 and N2O emissions may nevertheless exist).
Where calculated, CH4 and N2O emissions are converted into kg CO2e - a standardized unit representing the effect of a unit kg of CO2 on atmospheric warming - using the appropriate global warming potential for each respective gas.
Activity data required
According to this methodology, greenhouse gas emissions are directly proportionate to the distance travelled, which therefore must be specified in order to make an emissions calculation.
If multiple passengers are under consideration, this number can be additionally specified. The number of passengers is implicitly set to 1 by default, and therefore if no number if specified the returned emissions are those based on a single passenger.
Calculation and result
The returned quantities for this methodology represent CO2, CH4, N2O and CO2e emissions associated with the activity data (distance, passengers) specified.
CO2e emissions represent all three gases, converted using these global warming potential). The individual quantities for CH4 and N2O represent absolute quantities rather than CO2e quantities. For some scenarios within this methodology, emissions factors for CH4 and N2O are not available. In these cases values of zero are returned for the respective gases together with a notification comment. CO2 and CO2e values are returned as normal.
Other Greenhouse Gas Protocol transport methodologies are available representing general transport fuel consumption, fuels consumed in specific transport contexts, freight transport, and road transportation in the UK (with heavy goods), US and other regions.
The CO2 emissions factors contained within this methodology are presented in a mixture of units (i.e. kg [emissions] per mile; kg [emissions] per kilometer) in the original Greenhouse Gas Protocol source documentation.
For consistency, all CO2 factors are presented within the CarbonKit platform in a common default unit: kg [emissions] per mile. Emissions factors were converted using the kilometer-to-mile conversion factor provided in the Reference - EF Fuel Use worksheet of the source documentation, i.e.
emission factor kg per mile = emission factor kg per kilometer * 1.609344 kilometers per mile
Users of CarbonKit can, of course, choose to specify their consumption in any appropriate unit with CarbonKit handling any required conversions.