Maybe the missing tag was the problem, i don´t know. Thanks anyway!
By the way: "the routing" should avoid these roads, we agree. But since I am not able to change the routing-rules, I thought it would be pragmatic to restrict the access to everybody.
This road is an abandoned work access for roadworkers, so we should not spend too much time here.
On the other hand, tourists like me may end up here and getting no access to A63 - this should be avoided.