In the last
post, I illustrated the spatial adoption of Hybrid Electric Vehicles (HEVs)
across the local authorities of the UK. From a casual inspection of the
Choropleth map, it seems as if registrations appear to be highest in the south
east of England. A technique exists which allows us to determine if there is a
statistically significant spatial patterning in the registrations of HEVs. This
technique is called spatial autocorrelation analysis and considers if the
registrations of HEVs in a particular local authority are related to those observed
in neighbouring local authorities. A visual representation of spatial autocorrelation
is the Local Indicator of Spatial Association (LISA) map displayed below which
strips out all of the local authorities which do not appear to be connected to
their neighbours and concentrates on areas that are exhibiting significant
local patterning. The interpretation of the LISA is quite straightforward, with
regions highlighted in deep red (i.e. London) representing spatial hotspots for
HEV adoption whilst the regions highlighted in deep blue (i.e. the South West
England, Wales and the North of England) are characterised as spatial coldspots
of adoption.
A question
which naturally drops out of this assessment is why is London such an obvious
hotspot for the adoption of HEVs? One explanation is the presence of the London
Congestion Charge (LCC), which until recently had an exemption in place for
HEVs meaning that owners of these vehicles did not have to pay the daily fee to
enter the centre of London. To further evaluate whether the LCC has had an
effect over the registrations of HEVs, two approaches seem appropriate.
Firstly, we can see if the distance from the LCC seems to be connected with HEV
registrations. Secondly, we can consider if interaction with the LCC (measured
by the proportion of the populace who drive a car to work in the LCC) appears
to be connected with HEV registrations. These evaluations are presented in the
scatterplots below, and indicate that as distance from the LCC increases,
registrations of HEVs tend to decrease while as interaction with the LCC
increases, registrations of HEVs tend to increase. To summarise, it looks as if
the exemption of HEVs from the LCC has had a significant impact on the spatial
demand for these vehicles in the UK.
