Great Western Main Line

The Great Western Main Line is a main line railway in Great Britain that runs westwards from London Paddington station to the west of England and South Wales. The core Great Western Main Line runs from London Paddington to Temple Meads railway station in Bristol. A major branch of the Great Western, the South Wales Main Line, diverges from the core line west of Swindon and terminates in Swansea. The term "Great Western" is also used by Network Rail and other rail transport organisations in the UK rail industry to denote a wider group of routes, see Associated routes below.

The core London–Bristol Temple Meads line is the original route of the pre-1948 Great Western Railway which was subsequently taken over by the Western Region of British Railways and is now part of the Network Rail system.

History
The first section of the Great Western Railway was opened from London to a temporary station on the east side of the Thames at Maidenhead on 4 June 1838. The remaining line was opened in stages as the engineering works were completed:
 * Maidenhead to Twyford — 1 July 1839
 * Twyford to Reading — 30 March 1840
 * Reading to Steventon — 1 June 1840
 * Steventon to Faringdon Road — 20 June 1840
 * Faringdon Road to Wootton Bassett Road — 17 December 1840
 * Wootton Bassett Road to Chippenham — 31 May 1841
 * Chippenham to Bath — 30 June 1841
 * Bath to Bristol — 31 August 1840

The original broad gauge was supplemented  in various stages between 1854 and 1875 by a third rail to allow standard gauge  trains to operate over the route, but the broad gauge rail was retained until the last empty trains had been worked back from Penzance on 21 May 1892. The dates that the sections were mixed were:
 * London to Reading — 1 October 1861
 * Reading to Didcot – 22 December 1856
 * Didcot to Swindon – February 1872
 * Swindon to Thingley Junction, Chippenham – June 1874
 * Thingley Junction to Bathampton – 16 March 1875
 * Bathampton to Bristol — June 1874
 * Bristol station area — 29 May 1854

The original two tracks have been widened to four at several places:
 * Paddington to Southall — 1 October 1877
 * Southall to West Drayton — 25 November 1878
 * West Drayton to Slough — 1 June 1879
 * Slough to east side of Maidenhead Bridge — 8 September 1884
 * Maidenhead Bridge to Reading — 4 June 1893
 * Reading station — 1899
 * Reading to Pangbourne — 30 July 1893
 * Pangbourne to Cholsey and Moulsford —
 * Cholsey and Moulsford to Didcot — 27 December 1892
 * Various short sections between Didcot and Swindon, and at Bristol

Services
Main line and local services are provided by First Great Western (FGW). The stations served by express trains between London Paddington and Bristol Temple Meads are: Slough, Reading, Didcot Parkway, Swindon, Chippenham, Bath Spa and Keynsham. Not all trains call at all of these stations, especially Slough, Didcot and Keynsham.

Fast trains from Paddington to Heathrow Airport are operated by BAA as the Heathrow Express. Local services on this route are jointly operated by FGW and BAA under the Heathrow Connect name.

CrossCountry operate trains between Reading and Oxford, using the Great Western Main Line as far as Didcot and South West Trains operate a limited number of trains between Bath and Bristol.

First Great Western also operate a train between London Paddington – Cardiff Central (South Wales) every 30 minutes, with hourly extensions to Swansea. Additionally, 2–3 trains continue to Pembroke Dock on weekends during the Summer season to connect with ferry services to Ireland.

Infrastructure
The line speed is 125 mph, having been upgraded during the 1970s to support the introduction of the Intercity 125 (HST). The relief lines from Paddington to Didcot are currently limited to 90 mph as far as Reading, and then 100 mph to Didcot. Lower restrictions apply at various locations.

It is one of only two Network Rail-owned lines to be equipped with the Automatic Train Protection (ATP) system, the other being the Chiltern Main Line. Network Rail intends to replace the ATP system with ETCS – Level 2 in the future alongside the introduction of the new IEP trains.

The line is electrified at 25 kV AC overhead between Paddington and Airport Junction, the junction with the line to Heathrow Airport near Hayes.

Associated routes
Trains on the Great Western Main Line are sometimes diverted from Reading along the Reading to Plymouth Line as far as Westbury, from where they can use the Wessex Main Line to reach either Chippenham, or Bath Spa.

Beyond Bristol, some trains continue on the Bristol to Taunton Line to Weston-super-Mare or beyond.

The 2007 Network Rail Business Plan includes the following routes as part of their Great Western Main Line (Route 13):
 * Didcot to Oxford and Worcester via the Cherwell Valley Line and Cotswold Line
 * Swindon to Cheltenham Spa via the Golden Valley Line
 * Swindon to Cardiff Central and Swansea via the South Wales Main Line
 * Cross Country Routes south of Birmingham
 * All connecting branch lines.

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 (RUS) for the Great Western Main Line in 2005 to propose ways of meeting this demand. Network Rail planned to publish a new RUS by summer 2009; publication has been postponed to a scheduled date of early 2010, though a draft was issued for consultation in September 2009. In the meantime, their 2008 Business Plan highlights the large number of delays that can be reduced by improving the quality of the track, to which end a major renewal programme is underway from bases at Reading and Taunton. Further capacity improvements are also scheduled at Swindon, adding to recent changes and the new Platform 4.

Other more distant aspirations include resignalling and capacity improvements at Reading; the provision of four continuous tracks between Didcot and [Swindon (including a grade-separated junction at Milton, where the down (westbound) relief line switches from the north side of the line to the south); and resignalling between Bath and Bristol to enable trains to run closer together.

By 2016, there are plans for a direct rail link from Swindon to London Heathrow Airport. There are also calls for the reintroduction of a station at Corsham due to recent growth of the town. The original station was closed to passengers in 1965.

Reading station is currently undergoing a major redevelopment. Access to Heathrow Airport from the west remains an aspiration and there is a proposed future link to Heathrow Airport directly from Reading under the Heathrow Airtrack scheme which would use a route south of the Great Western Main Line. Under the plans for electrification of the Great Western announced in July 2009, it would make it easier to access Heathrow from Reading via the Great Western since the lack of electrification between Reading station and Heathrow Airport Junction near West Drayton station was a limiting factor.

Electrification
The line is electrified only between London Paddington and Airport Junction, which allows Heathrow Express and Heathrow Connect trains to operate. This electrification will be extended as far as Maidenhead as part of the Crossrail project. On 23 July 2009 it was announced that the Government plans to electrify the entire line to Bristol and also the line from Swindon to Swansea within the next eight years. This will coincide with the introduction of new Super Express trains. These will be electric trains, rather than diesel version previously planned. This is expected to lead to a decrease in journey times and will also potentially allow Crossrail services to be extended to Reading in the future.

The scheme announced by the Government on 23 July 2009 stated that, "work will begin immediately on the electrification of the Great Western Main Line between London, Reading, Oxford, Newbury, Bristol, Cardiff and Swansea, to be completed within eight years" (2016/2017). The electrified route will include the whole of the Great Western Main Line, the South Wales Main Line from Swindon to Swansea via the Severn Tunnel, and the connecting line from Bristol Parkway to Bristol Temple Meads stations. It is unclear if any parts of the line will be upgraded to a higher speed at the same time.

Network Rail plans to install European Rail Traffic Management System (ERTMS) in-cab signalling on the Great Western line, which is a pre-requisite to allowing the new Super Express trains to run at 140 mph. Some or all of the resignalling work will be carried out alongside the electrification work.

As of July 2010, the whole Great Western electrification scheme has been put on hold pending a return on investment review by the new government. Rail improvement plans announced by the new government on 25th November 2010 did not confirm this electrification plan. The plan to replace the Intercity 125 fleet, which dominates this line, include the possibility of continuing with diesel traction, implying electrification could be delayed indefinitely.

Route
Communities served: West London (including Acton, Ealing, Hanwell – Southall – Hayes – Harlington – West Drayton) – Iver – Slough – Langley – Burnham – Taplow – Maidenhead – Twyford – Reading – Tilehurst – Goring-on-Thames – Streatley – Cholsey – Didcot – Swindon – Chippenham – Bath – Keynsham – Bristol

The main line was designed by Isambard Kingdom Brunel and opened in stages by the Great Western Railway between 1838 and 1841. It was originally a broad gauge railway. Evidence of this can be seen at many places where bridges are a little wider than usual, or tracks ten feet apart instead of the usual six.

From London to Didcot, the line follows the Thames Valley, crossing the River Thames three times, including on the famous Maidenhead Railway Bridge. On this section, there are four tracks, grouped by speed with the "relief" lines on the north side of the "main" lines. Most smaller stations only have platforms in use on the relief lines. In August 2008, it was announced that a number of speed restrictions on the relief lines between Reading and London have been raised so that 86% of the line can be used at 90 mph, however the time allowed between stations for trains running on the relief lines has been reduced in the December 2008 timetable to improve timekeeping.

Didcot is home to the Didcot Railway Centre, a working steam railway museum. Soon after leaving Didcot, trains pass Didcot Power Station, a major source of freight traffic on the route with heavy coal trains running from Avonmouth near Bristol. Between Didcot and Wootton Bassett, there are a series of loop lines to allow fast trains to overtake slower ones. This section is also signalled for bi-directional running on each line but this facility is usually only used during engineering working or due to significant disruption to traffic in one direction.

Swindon, the next station, was the centre of the Great Western Railway and is still the headquarters for First Great Western. Leaving the station, trains pass the Swindon railway works on the north side of the line, now home to Steam - the Museum of the Great Western Railway. On the opposite side of the line is the "Railway Village", an area of industrial housing laid out for the employees of the railway workshops and a good example of early social housing.

At Wootton Bassett, the two different routes to Bristol — via Box Tunnel and via Bristol Parkway — allow flexibility. A third arrangement is to run via the Wessex Main Line but this involves a reversal at Bradford Junction so is only really suitable for multiple unit trains. A further diversionary route is available from Reading to Bath via Newbury.