Arun Valley line

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 and Arundel, before meeting the West Coastway line at Arundel Junction. Trains on the Arun Valley line then proceed to Portsmouth & Southampton.

Many stations on this line retain the short platforms which were originally built, not being extended by the Southern Railway when the line was modernized in the 1930s. This causes operational difficulties to this day, which require frequent platform and on-train announcements, telling passengers they must travel in the correct part of the train.

Wikipedia