What motor vehicles are prohibited from driving on a road where this sign is displayed?

The sign shown is a German traffic sign that prohibits certain slow-moving vehicles from entering the road. Specifically, it prohibits tractors and motor vehicles with trailers that have a maximum speed of 25 km/h or less.

The reason for this restriction is to prevent slow vehicles, which may cause traffic congestion or pose a danger on faster roads, from using roads where a higher minimum speed is required for safety and traffic flow.

Tractors or vehicles with a maximum speed over 40 km/h are not prohibited by this sign, as they can keep up with the general flow of traffic more safely.

So, the key rule to remember is: This sign bans slow vehicles (max speed 25 km/h) like certain tractors and motor vehicles with trailers from using that road. Vehicles capable of higher speeds are allowed.