This movie is based on the 'Ottifanten' comics by Otto, which are quite famous in Germany.
This was the first feature film job of Julian Hermannsen. Starting as an apprentice and quite soon ending up as the 3d sfx department for the movie as well as doing some of the compositing.
The cars were done in 3d as well as some special effects. SFX were mostly done for the interaction of the cars. Dust, debris, sand, oil and some other bits were done as sfx.
Work of Julian Hermannsen