"Rolling coal" isn't really a thing here in Oz but I can still smell a diesel long before I see it (or hear it, but I usually have my music up pretty loud).
Here in California, where people can call in gross polluters and have them removed from the roads, most of the stinky old diesels have gone away. As well, most of the old diesels are reaching the age where if you don't maintain them, they don't run. Yeah, the OM617 in that 300SD might keep going to a million miles, but the rest of the car won't and replacing all the stuff that wears out is getting to be a hobby. I've had to replace rear springs, I need to replace driver's seat springs, the upholstery is finally starting to crack (30 year old MB-TEX FTW) and so on. So people move on to something newer and cheaper to maintain. I very rarely see smoke coming out of even an older diesel any more, because most of those vehicles have fallen right off of the road.