From the previous
two posts discussing the structure of London’s car fleet in relation to the
proposed Emission Surcharge (also referred to as the T-charge) amendment to the
London Congestion Charge (which will see a £10 supplementary charge imposed on
cars that are not compliant to the Euro 4 emissions standard), we have seen
that a wide geographical variation in the registration levels of cars coming
under this regulation is present. The observation of geographical variation
does not necessarily mean that there is any inherent organisation in the
patterns which we see and could simply reflect a random allocation of cars
across the neighbourhoods of London. In order to test whether any spatial
organisation is present, we can conduct an analysis called a Local Indicator of Spatial Association (LISA) which determines if the registration levels of pre-Euro
4 vehicles in one neighbourhood is related to the levels observed in the
surrounding neighbourhoods. Thus, the LISA allows for spatial clusters which
share similar registration levels of cars not compliant to the Emission Surcharge
regulation to be identified.
The map
inserted above displays the results of the LISA and indicates that a series of
spatial clusters are present. Hotspots, which are shaded in dark red, represent
clusters which display relatively high levels of pre-Euro 4 car registrations.
The LISA indicates that hot-spots are present primarily in the mid-west of
London (both north and south of the Thames) as well as to the south-west of London.
Cold-spots, which are shaded in deep blue, represents clusters which exhibit relatively
low levels of pre-Euro 4 car registrations. The LISA implies that cold-spots tend
to be more common than hot-spots and have diverse locations across London. Indeed,
there doesn’t seem to be any clear splits in the clusters (e.g. North-South,
East-West, Interior-Exterior), which is likely due to the sporadic patterning
of London’s population.
