To arrive to the airport from the south of Barcelona (Castelldefels, Sitges, Vilanova, Tarragona...) you can go through the highway Pau Casals C-32, as it is drawn in the map.
Driving indications to arrive airport from the north of Barcelona are below, where besides you will be able to calculate the map with the most adequate routes from your position.
Consult your airline to know in advance which terminal you have to go, and follows the road's indications.
If you have to leave the car a time, consult Barcelona Airport parking fees