Kristiansand is a city in Norway.
West towards Stavanger
You can hitchhike from bus stops on the highway. But there are lots of tunnels.
The best spot is in the west part of the city, near the train station and ferry. You will follow a route under the highway, roundabout and about hundred metres (in way to Stavanger) there is bus stop and another tunnel behind it.
Or you can go about half a kilometre around the tunnel and there will be a petrol station.
A clearer possibility is to go the roundabout which splits the road to Møllevannsveien on one way and highway on the other. Most drivers are probably going shorter distance but DO NOT hesitate and take one of the cars, ask them to drop you off at a bus stop. You will have a better chance to get a ride and you won't be stuck there. It took cRosKy no more than 10 minutes to get picked up.