These are based on the official UK government greenhouse gas conversion factors, first calculated by DEFRA (the UK Department for the Environment, Food and Rural Affairs) in 2007 as follows:-
| Mode of Travel | CO2 Emission Factor Per km | Reference |
|---|---|---|
 Car / Van (CAR)* Taxi (TXI)* |
0.2042 kg CO2/vehicular km converted to 0.2042 kg CO2/passenger km |
Table 6 – Combined average for petrol & diesel cars |
 Car Share (CRS)* |
0.2042 kg CO2/vehicular km converted to 0.1021 kg CO2/passenger km |
Table 6 – Combined average for petrol & diesel cars |
 Public Service Bus (PSB) Dedicated School Bus (DSB) Bus Type Not Known (BNK) |
0.0891 kg CO2/passenger km | Table 8 – Bus |
 Train (TRN) |
0.0602 kg CO2/passenger km | Table 8 – National rail |
 Metro/Tram/Light Rail (MTL) |
0.0650 kg CO2/passenger km | Table 8 – Light rail & tram |
 London Underground (LUL) |
0.0526 kg CO2/passenger km | Table 8 – London Underground |
Source: ‘“Greenhouse Gas Conversion Factors For Company Reporting”, DEFRA (2007). (URL: http://archive.defra.gov.uk/environment/business/reporting/pdf/conversion-factors.pdf))
Notes:-
1. Per Vehicular Kilometre vs per Passenger Kilometre - The 2007 DEFRA figures quote the carbon emission factor for "Cars / Vans" in terms of kg CO2 per vehicular kilometre, whilst all the others are per passenger kilometres.
2. Evolution Of Calculation Factors Over Time - DEFRA first published an official list of emission factors in 2007, which was the same time as the STHC was being launched as a generally available service to all local authorities. Thus we adopted the DEFRA figures to calculate the school travel carbon footprints for the STHC. Since then however DEFRA have revised the figures just about every year as the science behind determining and measuring all the individual factors involved in greenhouse gas emissions has improved. With each revision however the calculation of the factors has become more complex, and not every factor is revised each time. To keep things simple therefore, and to enable "like-for-like" comparison between analysis years, we have continued to use the original 2007 figure in our STHC carbon footprint calculations. Figures for each revision are still available on the DEFRA website however so we invite you to investigate further, perhaps as a classroom project, to see what difference these revisions make to the calculated carbon footprint figure for your school.
Click on the following links to download each revision of the official DEFRA figures as an Adobe Acrobat (.pdf) document from the DEFRA website. The relevant figures are found in Annex 6: Passenger Surface Transport Emission factors in each document 2007, 2008, 2009 , 2010, 2011, 2012