Just doing the basics such as number plate recognition works well enough that the integration of these services has become a problem. I believe there is some controversy in the US about this now.
Surprisingly the combo of citric acid & baking soda makes a reasonable rust remover. I believe it is a chelating agent.
...and yes, it does fizz everywhere when mixing.
Like Tal said, a confounder for that would be distances driven. There are probably similar ones like rural/uban populations etc. It would be great to see a study allowing for these.
I couldn't find one but I didnt look very hard.
Why am I bold? why does markdown do my head in. Its really not that hard.