Complex sentence: This link was never built and the never-opened roundabout junction was adapted to provide access to the service area-however traffic travels the "wrong way" around the roundabout, hence some sharp turns on the slip roads.
Split into simpler sentences: This link was never built and the intended roundabout junction was not completed, instead being adapted to provide access to the service area. However traffic therefore travels the "wrong way" around the junction, with some sharp turns on the slip roads.