Carbon accounting for local authorities: A comparative analysis of NAEI estimates and MOT test data based estimates

The published national statistics for transport carbon emissions by local authority district are the National Atmospheric Emissions Inventory (NAEI). The NAEI uses the United Nations (UNFCCC) approach of attributing emissions to the territory from which they arise. For transport emissions, this means that (for example) the emissions from through traffic on the M6 and M42 as it passes through North Warwickshire district are attributed to North Warwickshire. In response to LAs’ complaints about this, a second data set is published for transport emissions, “CO2 emissions estimates within the scope of influence of Local Authorities”. For transport, emissions from railways and motorways are omitted, leaving emissions from A-roads and ‘minor roads’. This data set leaves strategic road network (SRNHighways England) roads classified ‘A’ in the data as ‘within the LA scope of influence’, even where they are expressways barely distinguishable from motorways in functional terms, eg the A14 in Kettering district. CREDS (ITS Leeds et al) has analysed a completely different data set, the annual mileage recorded at the annual MoT test. This allows a calculation of carbon emissions by all cars with their registered keeper living in a given LA district. (NB: The MoT data set does not at present include vans and lorries.) This paper explores aspects of the two data sets for the most easily available year, 2011.