Edit... but sincerely, I have no clue if it is trunk or primary.

Hi! It is quite difficult to tag 'correctly' road types in Catalonia, lots of discussion have been talked in the Spanish list. This is due to big differences between administrative classification and physical properties of the road. Specially in Catalonia many roads changed its name from Spanish classification to Catalan classification. C prefix only implies that the road is full administered by Catalan government. So there are C roads that are motorways and C roads that are ternary. Also with B, T, G and L roads.

Also political and cultural problems between Spanish and Catalan governments have made that N roads considered trunk roads in the rest of Spain (physically and administratively) are more like ternary roads (physically) than trunk in Catalonia.

Since this subject is much sensitive by so many people in Spain and Catalonia I beg you to tag with your unbiased common sense. Physically, C-31 south is like a motorroad trunk from Barcelona to Castelldefels, like a secondary from Castelldefels to Sitges (costes del Garraf - costes in roads mean in Catalan many many slow curves). I don't use this road further from Vilanova i la Geltrú but from aerial imaginary it seems more like a Spanish trunk with no motorroad tag than a primary (physically talking).

Yours,

Jaume.