About One-way streets, narrow single carriageways, separated carriageways and service roads: which statement is correct?
If your right-hand wheels leave the asphalt, the only risk is damage to tyres or rims; the steering stays under control.
A service road (ventweg) next to the main carriageway is simply an extra lane you can use for fast, through traffic.
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: exception omitted. Book p.61-62 - 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