Oh, dear, Woger, you're speaking from massive ignorance. The UK (and European) standards are _different_ from the US ones, more rigid in some respects and more lenient in others. So nothing that happened with regards to the US VW 'incident' has any bearing on your little taxi rank data point. That said, as always the current status quo is a function of past history, so that when the UK decided to promote fuel economy and low CO2 emissions that resulted in many more diesel vehicles. The US doesn't care about fuel economy and huge parts of the country doesn't believe in CO2 so they have many more ridiculously inefficient petrol engines. Additionally, while EU considers "ultra-low sulphur" diesel to be 10ppm, but in the US it's 15ppm for new engines. And so on.
Meanwhile, the biggest impact on your life caused by motor vehicles is the chance of being involved in a road traffic accident, which are at least twice as frequent in the US as in the UK, in large part due to the increased number of vehicles in use (i.e. the paucity of public transit).