The Impact of the London Congestion Charge on Hybrid Electric Vehicle Registrations

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.