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

This traffic sign indicates a prohibition for certain slow-moving vehicles. Specifically, it forbids tractors and motor vehicles with trailers that have a maximum speed of 25 km/h from driving on the road where this sign is displayed.

The rule behind this is to prevent slow vehicles, which could cause dangerous situations due to speed differences, from using roads designed for faster traffic. Tractors or vehicles with a type-specific maximum speed over 25 km/h, such as tractors capable of speeds above 40 km/h, are not affected by this prohibition and may use the road.

So, the sign is mainly about ensuring traffic flow and safety by restricting vehicles that cannot keep up with normal road speeds. Your answer correctly included tractors with a maximum speed of 25 km/h and motor vehicles with trailers of this speed, which are the vehicles prohibited here.