South Wales Main Line

The South Wales Main Line (Prif Reilffordd De Cymru) is a branch of the Great Western Main Line in the UK. It diverges from the core London-Bristol line at Wootton Bassett near Swindon, first calling at Bristol Parkway, after which the line continues through the Severn Tunnel into South Wales. Arriva Trains Wales operates regional and national services on the line in Wales. First Great Western operates High Speed Trains between London and South Wales and services between Cardiff and South West England. CrossCountry provides services from Cardiff to Nottingham via Gloucester and Birmingham.

History
The original route of the Great Western Railway between London and South Wales, after the opening of Brunel's Chepstow Railway Bridge in 1852, left the Bristol-bound Great Western Main Line at Swindon, proceeding via Stroud, Gloucester and Chepstow before rejoining the line as we know it today at Severn Tunnel Junction. This gave rise to the nickname 'Great Way Round'. In 1886, the opening of the Severn Tunnel brought the opportunity of a more direct route to South Wales, and trains from Swindon to Newport and beyond were routed via Bristol and the Severn Tunnel. This route leaves the one we know today at Wootton Bassett near Swindon rejoining it close to Patchway station. The route used today was established in 1903 with the building of what is often known as the Badminton Line. This involved the construction of about 33 miles of new track including two tunnels at Alderton and Sodbury between Wootton Bassett and Patchway. Not only did this provide a more direct route for traffic to and from South Wales, the gradient was easier for coal trains to negotiate, and it was perceived that the line would be a boost to what was, at the time of building, the expanding port of Fishguard, which was the GWR's connection to a point of departure for the United States of America by liner.

Infrastructure
There are four tracks from Severn Tunnel Junction through Newport to Cardiff Central, with two tracks on the remaining sections. Multiple-aspect signals are controlled from several power signal boxes including Swindon, Bristol, Newport and Cardiff. The maximum line speed from London to the Severn Tunnel is 125 mph; 90 mph from Severn Tunnel to Newport; 75 mph from Newport to east of Bridgend; 75 mph from east of Bridgend to Swansea Loop North junction; and 40 mph from Swansea Loop North Junction to Swansea.

Associated routes
Immediately west of Bristol Parkway is a complex of junctions that allow trains to leave and join the main line to South Wales. Trains from London to Bristol Temple Meads can run via the Badminton Line and Filton Abbey Wood, while trains from South Wales can use a curve between Patchway and Filton. The majority of these continue on the Wessex Main Line to Portsmouth, but some trains to London also use this route. An alternative diversionary route exists for when the Severn Tunnel is closed. This takes trains from Severn Tunnel Junction to Gloucester, from where they can rejoin the main line either by using the Golden Valley Line to Swindon, or by using the Cross-Country Route and reversing at Bristol Parkway. If the line is closed between Cardiff Central and Bridgend, an alternative route exists along the Vale of Glamorgan Line. Half of peak High Speed Trains trains and most off peak trains continue from Cardiff Central to Swansea, with a few continuing even further to Carmarthen. The local service between Swansea and Cardiff is branded Swanline. The urban network within and surrounding Cardiff, including on the Maesteg Line, is referred to as Valley Lines.

Future plans
Traffic levels on the Great Western Main Line are rising faster than national average, with continued increases predicted. The now defunct Strategic Rail Authority produced a Route Utilisation Strategy for the Great Western Main Line in 2005 to propose ways of meeting this demand, Network Rail plan to implement a new study in 2008. In the meantime, their 2007 Business Plan includes the provision of extra platform capacity at Cardiff Central, Newport and Bristol Parkway, also resignalling and line speed improvements in South Wales, most of which would be delivered in 2010-2014. Reading railway station is currently undergoing a major redevelopment and there is a proposed future link to Heathrow Airport directly from Reading under the Heathrow Airtrack scheme.

Electrification
The South Wales Main Line is one of the last of the major inter-city routes in Great Britain to remain un-electrified. The government announced in July 2009 a scheme to electrify the South Wales Main Line as part of a wider scheme of electrification on the Great Western Main Line. By 2017, the whole of the line will be electrified. The new Hitachi Super Express trains planned for the Great Western inter-city services will now be predominantly electric units instead of the planned diesel units. However, a proportion of the fleet will be using dual power source electro-diesel bi-mode trains, which will enable services to operate to Swansea before line electrification reaches Swansea. The bi-mode trains will allow inter-city services to operate from London all the way to Carmarthen in the future. The new Super Express trains will bring about an estimated 15% increased capacity during the morning peak hours. Electrification will cut journey times between Swansea and London by an estimated 19 minutes.

Communities served
Towns and cities served by trains from London: Settlements served by local trains only:
 * London
 * Reading
 * Didcot
 * Swindon
 * Bristol
 * Newport
 * Cardiff
 * Bridgend
 * Port Talbot
 * Neath
 * Swansea
 * Patchway
 * Pilning
 * Magor
 * Rogiet
 * Llanharan
 * Pontyclun
 * Pencoed
 * Pyle
 * Baglan
 * Briton Ferry
 * Skewen
 * Llansamlet