Hello, 
The RN188 must be classified as a trunk due to it's importance. The highway classfication was debated in our local community the last year, please follow our guidelines and/or ask in our telegram group  https://wiki.openstreetmap.org/w/index.php?title=ES:Argentina/V%C3%ADas_de_circulaci%C3%B3n#Rural
Thank you! Andrés