Carcassonne is a city in France. <map lat="43.225879907017" lng="2.3320613861093" zoom="16" view="0" float="right" />
West towards Toulouse
From the city center, follow the signs leading to the highway. It should be easy to get a ride at least to the toll booth (péage) from the roundabout at the end of Avenue Roosevelt (Rond-Point Georges Pompidou). It's a 2km walk from the city center. Alternatively, you can take bus No. 2 or 11, get off at Pompidou and continue walking for a few meters until you reach the roundabout.
If you're coming east from Toulouse, there is a service station about 20km west of Carcassonne along the A61. You can ask to be dropped off there; it is very busy and you will find people heading in many directions. In July 2016 there were rides available to Nîmes, Nice, Perpignan, Narbonne, Spain, and Lyon.