Not sure, but I think that in the Netherlands a municipality is not allowed to slap some 30kmh road signs along a roadway and call it a day. If the street does not 'communicate' that it is designed for that velocity, i.e. it is too broad, too many car lanes, then it must be adapted first to slow down traffic. There are a number of interesting design guidelines and manuals on the web, like CROW [0] for bicycle traffic, applied across the Netherlands.

[0] https://en.wikipedia.org/wiki/CROW_Design_Manual_for_Bicycle...