Well, turns out that speed limits for “trucks that carry passengers” appear in quite a few legislations, especially in the erstwhile Communist bloc countries and developing countries. Well, perhaps actually in the whole world except for the Western world.

See https://en.wikipedia.org/wiki/Combination_bus

For https://wiki.openstreetmap.org/wiki/Default_speed_limits , I added a column named truck_bus for now. Anyone have an idea / arguments for a better tag name?