I don`t know the situation especially in Stavanger but it is in many cities with ferry-lines the same problem.
If you have the ferry-berth directly in the city-center as like f.ex. in Stockholm (especially Viking Line), Kiel or Oslo or Göteborg today - the space for trucks, trailer and cars is limited and logistics maybe complicated. But if you go outside of the city-center with the ferry-port as f.ex. in Newcastle, Amsterdam, Rostock or Lübeck - the way for passengers to the city-center, bus- and train-centralstations is very long and very unattractive. F.ex. if you do a "kryssning" with DFDS to Newcastle you loose there much more than 2 hours in fact of the time for shopping and sightseeing because the bus must wait for the last slowly person, so i have tried this one time in the 90ies and will do it never again... .
I think that often it will choosen the easiest solution - with priority for freight, but not the best solution for all.
To go far outside where is a lot of space is easy. But why not to think about other solutions in the city-center ?
F.ex. with "Leichtbau-Parkhäuser" - these are cheap and fast to built - f.ex. this here on the picture can take 500 cars in waiting-lanes if the groudfloor takes 100. So you have won 80% more space in the port-area and can use it for more trucks.
https://www.goldbeck.de/fileadmin/_processed_/8/5/csm_Parkhaus_Innzeit_0958_01_6e5dfab45d.jpg
Is also possible a combination with "waiting-lane-parkhouse" and a terminal-building, offices from the port and ferry-company and a green-fassade outside. So many ground-space in the port-area won. F.ex. in Australia there are big modern parking-house integrated in shoppingcenter, apartments etc. also - so if Göteborg want to use the actually Stena-Line-area in another way - it would be possible to do this WITH the ferry-terminal integrated also.
Another possibility is to take more space from the waterside = build a parking-space into the port-berth, f.ex. in Ancona this is done (see the parking space around the "Restrooms WC Ancona-Port Bagni" in Google-Maps - there is the waiting-space for cars for the ferries - later built especially for this reason - one side of the ships is waiting-space for the trucks - the other side for cars).
https://www.google.com/maps/place/A...80543fc5ac!8m2!3d43.6158299!4d13.518915?hl=de
So it is very sad that the big city Göteborg soon will loose all the ferry-passengers / ferry-cruise-passengers. With any bus from Arendal ferry-berth through the freight-harbour the long way to the city-center - this is only a solution for some "hardcore-backpackers" in the Interrail-style from the 80ies... .
But maybe a new chance again for a ferry or new Katamaran-line Frederikshavn/Skagen - Lysekil/Frederiksstad/Moss ?
If the Stena-ferries do not go anymore in the city-center of Göteborg one big advantage of this route is lost and there is maybe a good chance for new competitor north of Göteborg. Especially to Frederiksstad or Moss would be including 100% tax-free money for the ferry-company.