All top-selling cars break emissions limits in 'real world' tests

This HN headline should be changed to "All top-selling diesel cars break..." as it is misleading. The Guardian article and the testing results it reports on are specifically related to diesel cars only.

Combine these results with the VW scandal and it's hard to see how the production of diesel passenger vehicles will continue for much longer, even in Europe, if these are the best real-world results that car manufacturers can achieve. The average emissions of NOx from these diesel vehicles were over five times the new Euro 6 legal limit.

Goodhart's law in action. Diesel engines get scored based on their performance in very specific circumstances, so they get built to score well in those specific circumstances.