So that's a pretty significant conclusion to draw without any hard data on the "tuned-ness" of a car. I wonder how much could be attributed to old cars instead

So that's a pretty significant conclusion to draw without any hard data on the "tuned-ness" of a car. I wonder how much could be attributed to old cars instead. That's something that would be easily measured by identifying the cars. But that may open a different can of worms if they determine people with the oldest cars are the biggest polluters* because it could be seen as an attack on the poor. * Odds are the old cars are the biggest polluters.. less efficient to start with, more likely to be out of tune, more worn parts, etc. But I don't have any data to state that as a conclusion.