The emissions methodology is based upon emissions factors which describe the rate at which heavy goods 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.
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).
The rate at which heavy goods vehicles emit greenhouse gases varies depending on the vehicle's fuel 'efficiency' (i.e. the distance acheived per unit of fuel consumed) which is affected by vehicle size and the loading of goods. Therefore, emissions factors for a broad range of generalised heavy goods vehicles and illustrative loadings are provided.
A total of 23 specific types of heavy goods vehicle scenarios are represented and are differentiated by vehicle type (rigid versus articulated), size (i.e. gross weight in tonnes), and percentage laden (0%, 50%, 100% as well as the UK average for each vehicle type).
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
Other DEFRA vehicle-based methodologies available represent vehicles differentiated by size and cars differentiated by market segment. 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 and loading scenario which best represents the users emissions scenario must be specified by making selections from each of the type, size and load 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.
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
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.