Core: Direction of travel and overtaking bans: D-signs and F-signs

The D category (Book p.241) regulates mandatory directions of travel. D1 belongs to a roundabout: you follow the indicated direction around the central island. D2 requires drivers to pass the sign on the side the arrow shows — for example at a speed bump or obstacle. D4 and D5 show one arrow: that arrow IS the duty, literally the direction shown on the sign, not a fixed meaning tied to the code itself. D6 and D7 show two or more arrows and offer a choice: you must follow one of the shown directions, but which one doesn't matter — both are equally valid. The F category regulates specific overtaking bans, and the precision lies in the target group. F1 bans motor vehicles from overtaking EACH OTHER — two cars, or a car and a truck. Because mopeds are legally not motor vehicles, a car may simply pass a moped rider under an F1 sign; that is not 'overtaking a motor vehicle'. F3 is even more specific: it only bans TRUCKS (motor vehicles with a permitted maximum mass over 3500 kg) from overtaking motor vehicles. A car may therefore simply overtake another car under an F3 sign; the sign is not addressed to it.