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There is Benutzungspflicht on the cycle lanes designated with the blue sign.
They're for when the road is deemed really dangerous so bikers stay off and get their own lane.
This is actually really cool (I love having my own lane / only have to share it with fellow cyclists not cars) - but only if there is a proper nice cycle path.
Like in Munich for example -there (often) the road is completely seperate from the cycle path, the tarmac is smooth as butter, it's actually a real joy to ride on these.
The main issue I have with cycling in Germany is the Benutzungspflicht. It's a really really bad idea as it allows people to banish cyclists from the roads. Which is the whole point, of course, so not that bad an idea from that perspective.