What must a motor vehicle's maximum speed, determined by its construction, be at least if you want to use this road?

This sign indicates a road reserved for motor vehicles ("Kraftfahrstraße"). According to German traffic rules, only motor vehicles that can reach a minimum construction-related maximum speed of 60 km/h (61 km/h in the answer) are allowed to use such roads. This limit ensures that slower vehicles, which might obstruct traffic flow, are not permitted. The rule helps maintain safe and efficient traffic movement on these roads, which are designed for faster travel.