Thanks for your comments.
Sorry I should have been clearer. I came across all of them in Overpass when I was trying to understand how to map kerbs.
There are 12,614 examples of kerb=* without barrier=kerb that are on roads: Overpass query I don’t think people meant to say that there is a barrier=kerb on the road that cars have to drive over (I’m not counting service roads here, for driveways this may be common in some places). I’m not trying to encourage anything, just documenting. Could add a warning that this usage is controversial? Have a look also at my previous thread on the topic.