The
South Wales Railway was built to carry traffic from
Gloucester to the strategic port of
Milford Haven and capture the lucrative
transatlantic maritime trade as well as communication with
Ireland. At Gloucester, the South Wales Railway met with the
Great Western Railway (GWR) which formed a route between London and South Wales after the opening of
Brunel's
Chepstow Railway Bridge in 1852. The original route of the GWR 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 circular route gave rise to the nickname 'Great Way Round'. GWR officials realised that the journey time between the South Wales Main Line and the Great Western Main Line could be significantly shortened by the construction of a tunnel directly underneath the
River Severn, which would be faster than the
ferry service between
Portskewett, Monmouthshire and
New Passage, Gloucestershire. The tunnel's construction was time consuming and disrupted by water infiltration, yet proceeded nonetheless. The completed tunnel was opened to regular goods trains during September 1886; the first passenger train followed on 1 December 1886. The opening of a more direct route to and from
South Wales led to trains from Swindon to
Newport and beyond being thereafter 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. This involved the construction of about 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. During the
British Rail era, the line was incorporated into the
Western Region and
steam locomotives were replaced by
diesel locomotives. Perhaps the most significant change occurred in 1976 in the form of the
Intercity 125, a new high speed train fleet that regularly ran at speeds of up to that was first introduced in the
Western Region. The Intercity 125 would remain in use into the twenty-first century and marked a considerable improvement in service. 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 ,
Newport and , together with resignalling and line speed improvements in South Wales, most of which would be delivered in 2010–2014.
Electrification The South Wales Main Line was one of the last of the major inter-city routes in Great Britain to remain un-electrified. In 2012, the British government announced it would proceed with work 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, the first electric trains began operating through the Severn Tunnel in June 2020. The electrification was originally intended to reach Swansea, but this was cancelled in July 2017. 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. ==Infrastructure==