The Arun Valley line, also known as the Mid Sussex line, is part of the Southern- and Thameslink-operated railway services. For the initial part of the route trains follow the Brighton Main Line, and at a junction south of Three Bridges the route turns westwards. It then runs via Crawley, Horsham (where there is a junction with the Portsmouth Line) and Arundel, before meeting the West Coastway line at Arundel Junction. Trains on the Arun Valley line then proceed to either Bognor Regis, Portsmouth Harbour or Southampon Central