SkiBob
I travel the N340 down to castellon, valencia and Benidorm from Vinaros. I assure you there is nothing like a dual carriageway until you get to the north of Valencia. However, you could travel south on the N340, turn right just before Torreblanca, past the new (old) airport, and then pick up the cv10 to valencia.  It is not a direct route. The transport ministry recommends that HGVs use this route, or the AP7