About One-way streets, narrow single carriageways, separated carriageways and service roads: which statement is WRONG?
A sign usually indicates which carriageway to follow; if there are no signs, you must keep right and therefore follow the right-hand carriageway.
The main road is intended for fast and through traffic, the ventweg for slow and local traffic (sign C5 at the entrance).
The prohibition applies to reversing as a driving manoeuvre along the road and to U-turns; backing into a parking space is explicitly still allowed.
If your right-hand wheels leave the road surface on a narrow single carriageway, you can simply steer calmly back to the middle.
Explanation
trap: edge-drop risk underestimated. Book p.64 - watch out for a sharp edge and/or a lower-lying verge on narrow single carriageways outside the built-up area; if your right-hand wheels leave the road, you quickly lose control of your steering