About Direction of travel and overtaking bans: D-signs and F-signs: which statement is WRONG?
The duty is following ONE OF the directions shown on the sign — both displayed arrows are equally valid, there is no primary and fallback direction.
Sign D4 always means 'mandatory turn right'; the arrow shown is decoration, the code itself fixes the direction.
F3 specifically bans TRUCKS from overtaking motor vehicles, not cars or other drivers.
F1 bans motor vehicles from overtaking EACH OTHER; mopeds are not motor vehicles, so passing a moped rider does not fall under it.
Explanation
trap: code-bound direction confused with arrow-bound direction. The duty is **the direction shown on the sign** — the arrow determines the direction, not the code itself; the same code D4 can point a different way with a different arrow