The Arun Valley Line, also known as the Mid Sussex Line, is part of the Southern-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 Mole Valley Line) and Arundel, before meeting the West Coastway Line at Arundel Junction. Trains on the Arun Valley Line then proceed to Portsmouth & Southampton.