The T-Charge: How does the Registration Rate of Pre-Euro 4 cars in London Compare to rUK?

With the proposed T-Charge amendment to the London Congestion Charge likely to lead to the introduction of a supplementary fee for cars which do not meet the Euro 4 emission standards, one issue to consider is if London has particularly high registration levels of non-compliant cars compared to the rest of the United Kingdom (rUK). A simple histogram of the registration rates of pre-Euro 4 cars across all of the neighbourhoods (lower super output areas) of the UK is presented in the figure below and displays a clear bell-shaped distribution, with the average registration rate of pre-Euro 4 cars being 35.5% with a standard deviation of 9.6%.

The boxplots in the figure below takes this cumulative distribution and separate it out by the Government Office Regions of the UK. Here, we see that the neighbourhoods of London tend to have higher levels of pre-Euro 4 car registrations compared to the other Government Office Regions. The difference is quite substantial when we compare highest to lowest, with London displaying an average of 41.9% registration rate of pre-Euro 4 cars whereas Scotland displays an average of 24.8%. One interpretation of this difference is that Scotland tends to have a much younger car fleet compared to London.