DEFRA road transport methodology by vehicle size

[edit / update model]

This methodology represents greenhouse gas emissions associated with the use of road vehicles as differentiated by their size. The data and calculation methodology originates from the UK government department DEFRA, as published in their most recent greenhouse gas (GHG) conversion factors documentation.

The methodology

Emissions model

The emissions methodology is based upon emissions factors which describe the rate at which road vehicles emit greenhouse gases according to distance travelled. These emissions factors represent emissions associated with entire vehicles, which can be contrasted with similar transport-related emissions factors which describe emissions on per-passenger or per-unit-of-freight bases. Users can nevertheless choose to 'share' vehicular emissions amongst passengers by specifying the vehicle occupancy.

Emissions - conventionally expressed in terms of mass (e.g. kg) - are calculated by simply multiplying these rates (mass emitted per distance; e.g. kg CO₂ per km) by a distance travelled (e.g km).

Model data

The rate at which road vehicles emit greenhouse gases varies depending on factors such as the type of fuel used, and the fuel 'efficiency' of the vehicle (i.e. the distance acheived per unit of fuel consumed). Therefore, emissions factors for a broad range of generalised vehicle types are provided.

A total of 36 specific types of road vehicle are represented and are differentiated by their vehicle type (e.g. car, motorbike or van), their fuel type (e.g. petrol, diesel, or several others), and a measure of their size. In the case of petrol and diesel cars and motorbikes, 'size' represents engine size (in litres and cubic centimetres respectively), while vans are differentiated on the basis of their gross vehicle weight. Cars which run on compressed natural gas (CNG), liquefied petroleum gas (LPG), or hybrid or unknown energy sources are differentiated according to qualitative size categories (e.g. 'small', 'medium').

Each vehicle type is represented by six distinct emissions factors which differentiate greenhouse gas emissions into the following types:

direct CO₂ emissions: carbon dioxide emissions produced during vehicle usage, i.e. fuel combustion
direct CH₄ emissions: methane emissions produced during vehicle usage, i.e. fuel combustion
direct N₂O emissions: nitrous oxide emissions produced during vehicle usage, i.e. fuel combustion
total direct emissions: all direct emissions, i.e. CO₂ + CH₄ + N₂O
indirect emissions: emissions associated with stages in the fuel production chain such as raw material extraction and fuel delivery
total or 'life cycle': the total of direct and indirect emissions

Each of these emissions factors are expressed in terms of kg CO₂e per km.

Similar methodologies

Other DEFRA vehicle-based methodologies available represent cars differentiated by market segment and heavy goods vehicles. Methodologies oriented around passenger and freight transport are also available.

Using this methodology

Choosing a specific activity type

To use this methodology, the particular type of vehicle which best represents the users emissions scenario must be specified by making selections from each of the type, fuel and size drill down choices.

Activity data required

According to this methodology, greenhouse gas emissions are directly proportionate to distance travelled which therefore must be specified - using the distance profile item value - in order to make an emissions calculation.

In addition, the number of vehicle occupants can be specified by setting the appropriate value using the occupancy profile item value (default = 1).

Users can choose to specify their activity data in a comprehensive range of appropriate units.

Calculation and result

The returned emissions quantities for this methodology are inclusive of CO₂, CH₄ and N₂O. The following discrete amounts are returned:

CO2: CO₂ emissions
methaneCO2e: CH₄ (methane) emissions
nitrousOxideCO2e: N₂O (nitrous oxide) emissions
totalDirectCO2e: total direct emissions
indirectCO2e: Indirect emissions
lifeCycleCO2e: Full life cycle emissions

Users should note that all quantities (including the separated CH₄ and N₂O emissions) are expressed in terms of CO₂e - the quantity of CO₂ which would exert the same atmospheric warming effect and the emissions quantity.

This methodology represents per vehicle emissions and therefore the returned emissions should be considered - by default - to represent those attributable to an entire single vehicle, or its sole occupant depending on the viewpoint of the user (the default value for vehicle occupancy is 1). If multiple vehicle occupancy is specified - by setting the occupancy profile item value to a positive value other than 1 - total vehicular emissions are shared between all occupants and therefore the returned emissions quantity represents the emissions attributable to each occupant.

UID	Label
ICW5Q6GFIEQ3	car, cng, average

type

Distance travelled

Vehicle occupancy