South Wales Main Line

The South Wales Main Line (Welsh: Prif Linell De Cymru), originally known as the London, Bristol and South Wales Direct Railway or simply as the Bristol and South Wales Direct Railway, is a branch of the Great Western Main Line in Great Britain. It diverges from the core London-Bristol line at Royal Wootton Bassett beyond Swindon, first calling at Bristol Parkway, after which the line continues through the Severn Tunnel into South Wales.

South Wales Main Line
Sodbury Railway Tunnel west exit in Old Sodbury (geograph 6554544).jpg
The entrance to the Chipping Sodbury Tunnel with the newly electrified overhead line equipment
OwnerNetwork Rail
LocaleSouth Wales
South West England
TypeHeavy rail
SystemNational Rail
Operator(s)Transport for Wales
Great Western Railway
Opened1850; 173 years ago (1850)
1903; 120 years ago (1903)
Line length84 miles 30 chains (135.79 km)
Number of tracksMainly double track, though quadruple track from Severn Tunnel Junction via Newport to Cardiff Central.
CharacterMain line
Track gauge4 ft 8+12 in (1,435 mm) standard gauge
Electrification25 kV 50 Hz AC OHLE
(Wootton Bassett to Cardiff Central)
Operating speedUp to 125 mph (201 km/h) in England
Up to 100 mph (161 km/h) in Wales
Route map
South Wales Main Line.png
(Click to expand)

Great Western Railway operates Class 800 trains between London and South Wales, and "Castle class" High Speed Trains on services between Cardiff and South West England. CrossCountry provides services from Cardiff to Nottingham via Severn Tunnel Junction and thence the Gloucester to Newport Line via Gloucester and Birmingham. Transport for Wales operates services between South Wales, and North Wales and the Midlands on the line.

The line between Swindon and Cardiff Central was electrified using the 25 kV AC overhead system as part of the larger electrification of the Great Western Main Line.


The original route of the Great Western Railway (GWR) 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 present line at Severn Tunnel Junction. This gave rise to the nickname 'Great Way Round'.[1][2]

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 Bath, Bristol and the tunnel.

The route used today was established in 1903 with the building of what is often known as the Badminton Line.[3] This involved the construction of about 33 miles (53 km) of new track, and tunnels at Alderton and Sodbury. The new line left the Bath line beyond Swindon at what is now Royal Wootton Bassett, rejoining the earlier route north of Bristol near Patchway. Not only did this provide a more direct route for traffic to and from South Wales, the gradients were easier for coal trains to negotiate, and it was thought that the line would be a boost to what was, at the time of building, the expanding port of Fishguard. This was the GWR's connection with trans-Atlantic ocean liner departures.

21st centuryEdit

In 2005, the Strategic Rail Authority produced a Route Utilisation Strategy for the Great Western Main Line in 2005 to propose ways of meeting increased traffic levels. Network Rail's 2007 Business Plan included the provision of extra platform capacity at Cardiff Central, Newport and Bristol Parkway, together with resignalling and line speed improvements in South Wales, most of which would be delivered in 2010–2014.

Reading station underwent a major redevelopment, being reopened in July 2014.[4]


Electrification work at Cardiff Central in October 2019

The South Wales Main Line was one of the last of the major inter-city routes in Great Britain to remain un-electrified. The government announced in 2012 a scheme to electrify the South Wales Main Line as part of a wider scheme of electrification on the Great Western Main Line. The line from London to Cardiff was fully electrified by Christmas 2019.[5]

The Hitachi Super Express trains bought for Great Western inter-city services are predominantly electric units, but a portion of the fleet are dual power source electro-diesel bi-mode trains, which enabled services to operate before line electrification is complete. The bi-mode trains will allow inter-city services to continue to operate from London all the way to Carmarthen in the future. The Super Express trains were expected to bring an estimated 15% increase in capacity during the morning peak hours. Electrification cut journey times between Swansea and London by an estimated 20 minutes, although electrification will not extend west of Cardiff to Swansea, Carmarthen or Pembroke Dock, and services on the line to Brighton, Portsmouth Harbour and Taunton will continue to be operated by diesel trains, as the Bristol to Exeter Line and the Wessex Main Line will not be electrified.[6]


Four track railway approaching Cardiff from Newport, prior to electrification

There are four tracks from Severn Tunnel Junction through Newport to Cardiff Central, with two tracks on the remaining sections.[7] Multiple-aspect signals are controlled from several power signal boxes including Swindon, Bristol and two in Cardiff. Over the August Bank Holiday weekend 2016, control of the signals between Westerleigh Junction and Pilning was switched over to the Thames Valley Signalling Centre. These signals now carry the prefix 'BL'.[citation needed]

The maximum line speed from Wootton Bassett Junction to Coalpit Heath is 125 mph (200 km/h);[8] 90 mph (145 km/h) from Coalpit Heath to Newport; 90 mph (145 km/h) from Newport to east of Bridgend;[9] 75 mph (120 km/h) from east of Bridgend to Swansea Loop North junction (with a small section of 100 mph (160 km/h) track through Pyle station); and 40 mph (65 km/h) from Swansea Loop North Junction to Swansea.[7]

Associated routesEdit

A diversionary route exists if the Severn Tunnel is closed. This takes trains from Severn Tunnel Junction to Gloucester, from where they can rejoin the main line either via the Golden Valley Line to Swindon, or take the Cross-Country Route and reverse 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 and most off peak trains continue from Cardiff Central to Swansea, with a few continuing to Carmarthen or in summer, Pembroke Dock.

The local service between Swansea and Cardiff is branded Swanline. The urban network within and surrounding Cardiff, including the Maesteg Line, is referred to as Valley Lines.

Communities servedEdit

Accidents and incidentsEdit

See alsoEdit


  1. ^ "South Wales Coastal" (PDF). Dovetail Games. Retrieved 2 October 2017.
  2. ^ "The Story of the G.W.R." Railway Wonders of the World. Retrieved 2 October 2017.
  3. ^ Kevin Robertson and David Abbott (1988). GWR The Badminton Line – A portrait of a railway. Sutton Publishing Ltd. ISBN 0-86299-459-4.
  4. ^ "Queen opens revamped Reading railway station". BBC News. 17 July 2014. Retrieved 10 February 2023.
  5. ^ "GWML electrification dates revealed". Retrieved 16 October 2017.
  6. ^ "Britain's Transport Infrastructure, Rail Electrification" (PDF). Department for Transport. Archived from the original (PDF) on 23 January 2017. Retrieved 16 September 2013.
  7. ^ a b "Network Rail – Wales Route Utilisation Strategy (November 2008)" (PDF). Archived from the original (PDF) on 7 June 2011. Retrieved 16 September 2013.
  8. ^ "Western Route Sectional Appendix December 2021" (PDF). Network Rail. 4 September 2021. Retrieved 21 December 2021.
  9. ^ Network Rail. "Network Rail: Route specifications 2011" (PDF). Network Rail. Archived from the original (PDF) on 30 January 2015. Retrieved 22 March 2015.

External linksEdit

KML is from Wikidata