The Butetown Branch Line, also known as the Cardiff Bay Line, is a railway line in South Wales from Cardiff Bay and Butetown to Cardiff city centre. The service pattern used to comprise a mixture of shuttle services along the branch and through trains along the Rhymney Line to Caerphilly, or the Coryton Line to Coryton, but since December 2005 is a shuttle service from Queen Street station only.
Originally, the branch was opened by the Taff Vale Railway In 1922, it was absorbed, along with the Rhymney Railway, into the enlarged Great Western Railway. After hanging on for survival in the 1970's and 1980's the initial phases of the regeneration of the Cardiff Bay area offered new hope for the branch. Signalling and track improvements offered an improved service in the early 1990's.
At privatisation in 1995, services were operated by the Cardiff Railway Company, which traded as Valley Lines. This was subsumed by the new Wales and Borders franchise in 2001, which was subsequently awarded to Arriva in December 2003 and operates as Arriva Trains Wales. The December 2005 timetable introduced a further increase in services to 4 trains per hour 18 hours a day, and even a Sunday service for the first time (further improved in June 2006 to offer the same 4 trains per hour service from 11am to 4pm). This makes a stunning turnaround in 30 years. In December 2005, Arriva employed a Class 153 to "shuttle" along the Butetown Line, upgrading from the notoriously rough riding Class 143 'Pacers' used for the service.
In July 2006 the service was due to be provided by a 1950s heritage British Rail Class 121 "Bubble car" DMU. The unit finally entered service in 17 August 2006, only to be withdrawn for repairs two days later. The unit then re-entered service on 14 September 2006.