There was no bike lane.
As far as I can remember: at the northern end of the highway there used to be a 237 road sign (cycle path), whilst there was no sign at the southern end.
Yes, I know that this is incorrect under German road traffic law but unfortunately the local authorities are often unwilling to take advice on many issues. When you raise such a matter, you usually get one of two responses: it’s not a priority, or there’s no money available for it.
Or you get no answer.