Car Defra By Size

This category allows users to calculate greenhouse gas emissions from a car journey from indicating the car's size. The methodology follows the latest Defra emission factors and advice.

How to use this category

There are two drill-downs in this category. Use the drill-down fuel to select the fuel used by the vehicle from the following options.

• petrol

• diesel

• petrol hybrid

• lpg

• cng

• average - for use if fuel is unknown

• small

• medium

• large

• average - for use if fuel is unknown

The distance must then be entered as a profile item value. There are four further optional profile item values, occupants, ownFuelConsumption, numberOfJourneys and totalFuelConsumed.

The occupants profile item value is used to enter the number of people in the car for the selected journey (default 1). The emissions are then divided by the number of occupants in order to return the fraction of the emissions due to each person. The ownFuelConsumption can be entered if the user has a reliable value for their vehicles fuel consumption (default units of km/L). If this is entered then it overrides Discover's default emission factors for the selected vehicle. The algorithm then divides the fuel emission factor, from the Fuel_Defra category, by the users ownFuelConsumption and multiplies by the distance. The numberOfJourneys profile item value (default 1) can be used if the specified journey has been repeated a number of times; the emissions for one journey are multiplied by this value. Finally, totalFuelConsumed can be entered if the volume of fuel used for the entire journey is known. In this case the volume of fuel is multiplied by the appropriate emission factor in the Fuel_Defra category.

Algorithm

If no fuel consumption information entered

CO2eEmissionFactor = CO2EF + CO2eEFForN2O + CO2eEFForCH4

CO2e = CO2eEmissionFactor * distance * numberOfJourneys / occupants

If ownFuelConsumption entered

CO2eEmissionFactor from business/energy/fuel

CO2e = (CO2eEmissionFactor / ownFuelConsumption) * (distance / occupants) * numberOfJourneys

If totalFuelConsumed entered

CO2eEmissionFactor from business/energy/fuel

CO2e = CO2eEmissionFactor * totalFuelConsumed

The algorithm returns a value of kgCO₂e for the particular journey, per occupant. This value includes contributions from carbon dioxide, nitrous oxide and methane.