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Fietsstraten (bicycle streets, streets where bicycles take priority over cars) are the future.
In practice the inner city of most Dutch towns is already overtaken by bicycles, cars are allowed, but have to slow down due to the large numbers of bicycles that take priority over the cars (regardless of traffic rules).
These signs make that official.
By arranging it in this manner, people can still take cars, but it's basically very slow. Not good for small distances in town. But when you really need, you can still take a car and be as slow as the slowest cyclists (and they are slow in this country).
Arranging it in this way is great. it discourages car-traffic, without having to prohibit anything. It doesn't make car-fanatics really angry, but still achieves the goals of other, more strict anti-car regulations.