TheGreat Western Main Line (GWML) is amain linerailway in England that runs betweenLondon Paddington andBristol Temple Meads. It connects to other main lines such as those fromReading to Penzance andSwindon to Swansea. The GWML is presently a part of the national rail system managed byNetwork Rail, while the majority of passenger services upon it are provided by the currentGreat Western Railway franchise.

Great Western Main Line
Maidenhead Railway Bridge carrying the line over theRiver Thames.
Overview
Status	Operational
Owner	Network Rail
Locale	Greater London South East England South West England
Termini	London Paddington Bristol Temple Meads
Stations	25
Service
Type	Commuter rail,Higher-speed rail[1]
System	National Rail
Operator(s)	Great Western Railway, Elizabeth line, Heathrow Express, CrossCountry
Depot(s)	North Pole, Reading, St Philip's Marsh
Rolling stock	Class 158 Class 159 Class 165 Class 166 Class 220 Class 221 Class 345 Class 387 Class 800 Class 802
History
Opened	30 June 1841 (complete line)
Technical
Line length	118 miles 19 chains (190.28 km)
Number of tracks	Four (London to Didcot), two (Didcot to Bristol)
Track gauge	4 ft 8+1⁄2 in (1,435 mm)
Old gauge	7 ft 1⁄4 in (2,140 mm)
Electrification	25 kV 50 hz ACOLE (London to Chippenham)
Operating speed	125 mph (200 km/h)
Signalling	AWS,TPWS,ATP
Route map

v t e Great Western Main Line
Legend
miles Circle andHammersmith & City lines viaLiverpool Street Elizabeth line toAbbey Wood andStratford 0⅓ London Paddington Paddington Goods Royal Oak () Mileage Yard Goods & Coal Subway Junction Westbourne Park () Portobello Junction Notting Hill Sidings Circle andHammersmith & City lines toHammersmith Kensal Green Gasworks siding Westway (A40) West London Line North Pole depot West London Junction Old Oak Common TMD Old Oak Common Goods Old Oak West Junction Acton–Northolt line Willesden & Acton Brick Co. siding Central line viaLiverpool Street North London line Central line Western Avenue (A40) 4¼ Acton Main Line Central line District andPiccadilly lines 5¾ Ealing Broadway 6½ West Ealing Greenford branch line Plasser works 7¼ Hanwell Wharncliffe Viaduct overRiver Brent Brentford branch line 9⅓ Southall Grand Union Canal 11⅓ Hayes & Harlington Airport Junction toHeathrow Airport stations 14⅓ West Drayton River Colne Greater London boundary Uxbridge (Vine Street) branch line Staines and West Drayton Railway to Colnbrook Cargo Centre M25 motorway 14¾ Iver Western Rail Approach to Heathrow toHeathrow Terminals 2 & 3 andTerminal 5 (proposed) 16¼ Langley 18½ Slough Slough–Windsor & Eton line 21⅓ Burnham 22½ Taplow Jubilee River Maidenhead Railway Bridge overRiver Thames 24¼ Maidenhead Marlow branch line 31⅓ Twyford Henley branch line River Loddon Sonning Cutting 1 mile (1.6 km) long 60 feet (18 m) deep River Kennet Waterloo–Reading line North Downs Line Reading East Junction 36⅓ Reading Reading–Basingstoke line andReading–Taunton line 38¾ Tilehurst Purley Cutting 41½ Pangbourne Gatehampton Railway Bridge overRiver Thames 44¾ Goring & Streatley Moulsford Railway Bridge overRiver Thames Moulsford 48½ Cholsey Cholsey & Wallingford Railway (bank holidays and weekends only) Didcot, Newbury and Southampton Railway 53⅓ Didcot Parkway Didcot Railway Centre Cherwell Valley line toOxford,Birmingham and theCotswold Line Didcot power stations Milton Park estate Steventon Wantage Tramway Wantage Road Challow Uffington Faringdon branch Shrivenham Stratton Park Halt Highworth branch line 77¼ Swindon Golden Valley line toCheltenham Spa andBirmingham Midland & South Western Junction Railway M4 motorway Wootton Bassett Junction South Wales Main Line Dauntsey Malmesbury branch line Christian Malford Halt Calne branch line 94⅓ Chippenham Thingley Junction Wessex Main Line toMelksham,Bradford-on-Avon andSalisbury Corsham Box Tunnel 2939 yd 2687 m Box (Mill Lane) Halt Box Bathford Halt Bathford Bridge overRiver Avon Wessex Main Line toWeymouth,Southampton andBrighton Bathampton Junction Bathampton Hampton Row Halt 107⅓ Bath Spa 108⅓ Oldfield Park Somerset & Dorset Joint Railway Twerton-on-Avon Twerton Tunnel Saltford Tunnel Saltford 113¾ Keynsham St Anne's Park No 3 Tunnel 1017 yd 930 m St Anne's Park No 2 Tunnel 154 yd 141 m St Anne's Park River Avon North Somerset Junction Bristol & North Somerset Railway St Philip's Marsh TMD Cross Country Route toGloucester &Birmingham New Street toMangotsfield toAshton Gate Platform 116½ Bristol Temple Meads Bristol West Junction Temple Meads Goods Bristol–Exeter line

The GWML was built by the originalGreat Western Railway company between 1838 and 1841, as a dual track line in the7 ft (2,134 mm)broad gauge. The broad gauge remained in use until 1892, after which standard gauge track has been exclusively used. Between 1877 and 1932, many sections of the GWML were widened to four tracks. During 1908,Automatic Train Control (ATC) was introduced as a safety measure. In 1948, the Great Western Railway, and thus the GWML, was merged into theWestern Region of British Railways.

During the 1970s, the GWML was upgraded to support higher line speeds, as a result of which many sections permitted 125 mph (201 km/h) operations, enabling the newly introducedInterCity 125 high speed train (HST) to make faster journeys.British Rail proposed widespread electrification of the line in the late 1970s, although this was not speedily implemented. During the mid-1990s, a stretch of the GWML between London Paddington andHayes & Harlington was electrified using25 kV AC overhead lines for theHeathrow Express. Further, although not total, electrification was carried out during the 2010s; this permitted the replacement of diesel-powered trains such as the InterCity 125 andClass 180 with electric andbi-mode train sets such as theHitachi Super Express high speed trains, specifically theClass 800 andClass 802. Due to budget overruns, the British government deferred electrification of the section throughBath Spa fromRoyal Wootton Bassett toBristol in 2016.

The route includes dozens oflisted buildings and structures, including tunnel portals, bridges and viaducts, stations, and associated hotels. Presently, the GWML is electrified between London Paddington and Royal Wootton Bassett. In the long term, Network Rail plans to installEuropean Rail Traffic Management System (ERTMS) in-cab signalling across the entire line.

The construction of what would become the GWML was motivated by several factors, one of the more influential being the sizeable merchant community of Bristol, which keenly advocated for such a railway to be built to help maintain the city's position as the second port of the country as well as the chief one for American trade.^[2] More specifically, fearing rising competition fromLiverpool and railway developments to its favour, the sought railway was to be preferably built to superior standards as to out-perform any of the lines serving theNorth West of England.^[3] Thus, the line built by theGreat Western Railway and engineered byIsambard Kingdom Brunel was originally a dual track line using a wider7 ft (2,134 mm)broad gauge.^[4] The line's construction costs were considerably higher due to the use of this broad gauge.^[5]

The route of the GWML includes dozens oflisted buildings and structures, including tunnel portals, bridges and viaducts, stations, and associated hotels.^[6] Part of the route passes through and contributes to theGeorgian Architecture of theCity of Bath World Heritage Site; the path throughSydney Gardens has been described as a "piece of deliberate railway theatre by Brunel without parallel".^[7]Grade I listed structures on the line includeLondon Paddington,Wharncliffe Viaduct, the 1839 Tudor gothicRiver Avon Bridge in Bristol, andBristol Temple Meads station.^[8][5]

The line was opened in stages between 1838 and 1841.^[9] The first section, between Paddington andMaidenhead Bridge opened on 4 June 1838; the final section, between Chippenham and Bath, was opened on completion of theBox Tunnel, the longest railway tunnel driven by that time, in June 1841.^[10][11] The line's alignment was so level and straight it was nicknamed "Brunel's billiard table".^[5]

The track was supplemented with a third rail fordual gauge operation, allowing standard gauge4 ft 8+1⁄2 in (1,435 mm) trains to also operate on the route, in stages between 1854 and 1875. Dual gauge was introduced as follows: London toReading (October 1861), Reading toDidcot (December 1856), Didcot toSwindon (February 1872), Swindon to Thingley Junction,Chippenham (June 1874), Thingley Junction toBathampton (March 1875), Bathampton to Bristol (June 1874), Bristol station area (May 1854). The broad gauge remained in use until 1892, at which point the last 500 miles of track were converted to standard gauge.^[5][12]

Between 1877 and 1899, the original dual tracks were widened to four in numerous places, mainly in the east half of the line: Paddington toSouthall (October 1877), Southall toWest Drayton (November 1878), West Drayton toSlough (June 1879), Slough to east side ofMaidenhead Bridge (September 1884), Maidenhead Bridge toReading (June 1893), Reading station (1899), Reading toPangbourne (July 1893), Pangbourne toCholsey and Moulsford (June 1894), Cholsey and Moulsford toDidcot (December 1892); also short sections between Didcot and Swindon, and at Bristol.^{[citation needed]}

Following theSlough rail accident of 1900, in which five passengers were killed, improvedvacuum braking systems were used on locomotives and passenger rolling stock; furthermore,Automatic Train Control (ATC) was introduced in 1908.^[13]

Further widenings of the line took place between 1903 and 1910; another round of widening works occurred between 1931 and 1932.^[14] By the 1930s, trains traversing the GWML were reportedly attaining the highest average speeds in the world.^[5]

A legacy of the broad gauge was that trains for some routes could be built slightly wider than was normal in Britain; examples included the 1929-builtSuper Saloons used on theboat train services that conveyed transatlantic passengers to London in luxury.^[15] When the company celebrated its centenary during 1935, new "Centenary" carriages were built for the Cornish Riviera Express, which again made full use of the widerloading gauge on that route.^[16]

At the outbreak of theFirst World War in 1914, the Great Western Railway, and thus the GWML, was taken into government control, as were most major railways in Britain. After the conflict, the companies were reorganised into the"big four" companies, of which the Great Western Railway was one. The railways, including the GWML, returned to direct government control during theSecond World War before beingnationalised to formBritish Railways (BR) in 1948, thus bringing the line into public ownership.^[17][18]

Unlike the other BR regions, which introduceddiesel-electric locomotives, theWestern Region, to which the GWML belonged, decided to procure a complete range ofdiesel-hydraulic locomotives to fulfil itstype 1 to type 4 power requirements. These included theWarship locomotives, which were based on provenWest German designs, the British-designedClass 14,Hymek andWestern types. However, these were all eventually withdrawn and replaced with more standard British Rail diesel-electric classes such as theClass 37 andClass 47.

During the 1970s, the line speed of the GWML was upgraded to permit faster operations; this work was in preparation for the introduction of theInterCity 125 high speed train (HST).^[19][20] The HST brought about considerable improvements in service and reduced journey times.^[21][22]

In 1977, the Parliamentary Select Committee on Nationalised Industries recommended considering electrification of more of Britain's rail network and, by 1979, British Rail had presented a range of options that included electrifying the line from Paddington to Swansea by 2000.^[23] Under the1979–90 Conservative governments that succeeded the1976–79 Labour government, the proposal was not implemented.

In the mid-1990s, the line between London Paddington andHayes & Harlington was electrified as part of theHeathrow Express scheme, which was officially launched in June 1998.^[24][25]

As part of theprivatisation of British Rail, the Great WesternInterCity franchise was awarded by theDirector of Passenger Rail Franchising toGreat Western Holdings in December 1995, and it began operations on 4 February 1996.^[26][27] Via multiple contract extensions, this operator, which currently trades asGreat Western Railway has been the primary operator of passenger services on the GWML for multiple decades.^[28][29][30]

In August 2008, it was announced that a number of speed limits on the relief lines between Reading and London had been raised, so that 86% of the line could be used at 90 mph (140 km/h).^[31]

By 2019, the partial electrification of the GWML permitted the replacement of InterCity 125 andClass 180 sets by newHitachi Super Express high speed trains – theClass 800 andClass 802. The procurement programme for these trains, known as theIntercity Express Programme, was highly impacted by the GWML's electrification scheme, particularly the abandonment of diesel-only trains in favour of bi-mode trains, which were elongated and outfitted with a second transformer to maximise their use of the electrified sections.^[32][33] The electrification of the line also allowed the introduction of other rolling stock, such asClass 387electric multiple units, to conduct shorter-distance services.^[34]

The main communities served by the Great Western Main Line areWest London (includingActon,Ealing,Hanwell,Southall,Hayes,Harlington andWest Drayton),Iver,Langley,Slough,Burnham,Taplow,Maidenhead,Twyford,Reading,Tilehurst,Pangbourne,Goring-on-Thames,Streatley;Cholsey,Didcot,Swindon,Chippenham,Bath,Keynsham andBristol.^[35]

From London to Didcot, the line follows theThames Valley, crossing the River Thames three times, including on theMaidenhead Railway Bridge. Between Chippenham and Bath the line passes throughBox Tunnel, and then follows the valley of theRiver Avon.

A junction west of Swindon allows trains to reach Bristol by an alternative route along theSouth Wales Main Line. Other diversionary routes exist between Chippenham and Bath viaMelksham and theWessex Main Line, although this involves a reversal at Bradford Junction; and from Reading to Bath via theReading–Taunton line.

Services of threetrain operating companies use the line:

• Great Western Railway (GWR) operates most services:^[36]
  • Inter-city trains run between London Paddington and Bristol Temple Meads, via Reading, Didcot Parkway, Swindon, Chippenham and Bath Spa; some services do not call at Didcot Parkway.
  • Inter-city services between London Paddington – Cardiff Central operate every 30 minutes, with hourly extensions to Swansea. At Swansea/Cardiff, there is a connectingTransport for Wales' boat train to/fromFishguard Harbour for theStena Line ferry toRosslare Europort in Ireland. An integrated timetable is offered between London Paddington and Rosslare Europort with through ticketing available.^[37] Daytime and nocturnal journeys are offered in both directions daily.
  • Heathrow Express trains from Paddington toLondon Heathrow Airport, on behalf ofHeathrow Airport Holdings.^[38]

• Elizabeth line services run on the Great Western Main Line between London and Reading.^[39]

• CrossCountry operates long-distance trains using the GWML between Reading and Didcot Parkway.^[40]

There are four tracks between London and Didcot, two in each direction. The main lines are mostly used by the faster trains and are on the south side of the route. The relief lines on the north side are used for slower services and those that call at all stations, as only London Paddington, Slough, Maidenhead, Twyford, Reading and Didcot Parkway stations have platforms on the main lines (although a few others have main line platforms that can be used in an emergency). Between Didcot andRoyal Wootton Bassett, a series of passing loops allow fast trains to overtake slower ones. This section is signalled for bi-directional running on each line but this facility is usually only used during engineering working or when there is significant disruption to traffic in one direction.^[41]

The summit of the line is at Swindon and falls away in each direction: Swindon is 270 feet (82 m) above Paddington and 292 feet (89 m) above Bristol Temple Meads. The maximumgradient between Paddington and Didcot is 1 in 1320 (0.75 ‰ or 0.075%); between Didcot and Swindon it is 1 in 660 (1.5 ‰ or 0.15%), but west of Swindon, gradients as steep as 1 in 100 (10 ‰ or 1%) are found in places, such asBox Tunnel and to the east ofDauntsey.^[42][43]

The line is electrified between Paddington and Langley Burrell (just east of Chippenham) using25 kV AC overhead supply lines; the Reading to Taunton line (as far as Newbury) and the South Wales Main Line (as far as Cardiff Central) are also electrified.

The line speed is 125 mph (201 km/h).^[44] The relief lines from Paddington to Didcot are limited to 90 mph (140 km/h) as far as Reading, and then 100 mph (160 km/h) to Didcot. Lower restrictions apply at various locations.^[41] The line is one of twoNetwork Rail-owned lines equipped with theAutomatic Train Protection (ATP) system, the other being theChiltern Main Line.^[45]

Major civil engineering structures on the Great Western Main Line include the following.^[46]

Line-side train monitoring equipment includes hot axle box detectors (HABD) andWheelchex wheel impact load detectors (WILD), sited as follows.^[46][47]

From 2011, the GWML underwent a £5 billion modernisation by Network Rail.^[48]

Reading station saw a major redevelopment with new platforms, a new entrance, footbridge and lifts; the work was completed a year ahead of schedule^[49] in July 2014.^[50][51]

Signalling Solutions resignalled the 12 miles (19 km) from Paddington toWest Drayton, including the Airport branch, as part of theElizabeth line.^[52]

The eastern section from Paddington to Hayes & Harlington was electrified in 1998.^{[citation needed]} TheCrossrail project covered electrification of the line from Airport Junction to Maidenhead and, following a number of announcements and delays, the government announced in March 2011 that it would electrify the line as far as Bristol Temple Meads.^[53][54][55]

Following delays to the work and a large increase in costs,^[56] the Conservative government announced in July 2017 that, for the time being, electrification would only be completed as far as Thingley Junction, 2 miles (3.2 km) west of Chippenham.^[57][58] Electrification as far asDidcot Parkway was completed in December 2017,^[59] and to Thingley Junction in December 2019.^{[citation needed]}

Electrification of associated lines, includingBristol Parkway to Temple Meads and Didcot to Oxford, was also postponed indefinitely; electrification of the route between London and Cardiff was completed in 2019.^[60] The government argued that bi-mode trains would fill in the gaps pending completion of electrification, although theClass 800 trains are slower in diesel mode than under electric power.

Network Rail plans to installEuropean Rail Traffic Management System (ERTMS) in-cab signalling on the Great Western line;^[61][62] this is a pre-requisite for theSuper Express trains to run at 140 mph (225 km/h).^[63] Some of this resignalling work was undertaken during the electrification work.^[61] Furthermore, Network Rail has envisaged the deployment of ERTMS to function as the replacement for the aging ATP system.^[64]

Further capacity improvements are also scheduled at Swindon, adding to recent changes and the new Platform 4.^{[citation needed]}

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 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.^{[citation needed]}

Access toHeathrow Airport from the west remains an aspiration and the 2009Heathrow Airtrack scheme, abandoned in 2011, proposed a route south of the Great Western Main Line to link the airport with Reading. Plans for electrification of the line will make it easier to access Heathrow from Reading, since lack of electrification between Reading station and Airport Junction (near West Drayton station) was a limiting factor.^[61] Plans under consideration in 2014 included new tunnels between Heathrow andLangley.^[65]

There are calls for the reintroduction ofCorsham station due to recent growth of the town.^[66] Theoriginal station was closed to passengers in 1965.

A local group is campaigning for the reopening ofSaltford station between Bath and Bristol, to coincide with electrification.^[67]

There have also been calls to reopen the formerWantage Road station.^[68]Oxfordshire County Council included a proposal for a new station to serve Wantage and Grove in their 2015–2031 local transport plan.^[69]

• Slough rail accident – 16 June 1900: An express train from Paddington toFalmouth Docks ran through two sets of signals at danger and collided with a local train heading forWindsor. Five passengers were killed and 35 seriously injured.^[70]
• Ealing rail crash – 19 December 1973: A train from Paddington to Oxford derailed after a loose battery box cover on theClass 52Western locomotive hauling the train struck lineside equipment, causing a set of points to move under the train. Ten passengers were killed and 94 injured.^[71]
• Southall rail crash – 19 September 1997: An InterCity 125 service from Swansea to Paddington, operated byGreat Western Trains, failed to stop at a red signal and collided with a freight train entering Southall goods yard. Seven people were killed and 139 were injured. The incident severely damaged public confidence in the safety of the rail system. It was found that the train'sautomatic warning system (AWS) was faulty, and the driver had been distracted (he had bent down to pack his bag). Great Western Trains was fined £1.5 million for violations of health and safety law in connection with the accident.^[72][73]
• Ladbroke Grove rail crash – 5 October 1999: AThames Trains service from Paddington toBedwyn passed a signal at danger at the gantry protecting a main set of (crossover) points between the one-way and bi-directionally used lines. The train ran the wrong way down the line and was hit head-on by aFirst Great Western HST service fromCheltenham Spa to Paddington at a closing speed of approximately 130 mph (210 km/h). 31 people died, including both drivers, with more than 520 people injured. Thames Trains was fined £2 million for violations of health and safety law.^[74]Railtrack pleaded guilty to charges under theHealth and Safety at Work Act 1974 in relation to the accident. It was subsequently fined £4 million and was also ordered to pay £225,000 in costs.^[75]

The reference for the route map diagram is:-Jowett, Alan (March 1989).Jowett's Railway Atlas of Great Britain and Ireland: From Pre-Grouping to the Present Day (1st ed.). Sparkford: Patrick Stephens Ltd. pp. 113, 115a, 116, 118b, 118d, 120,124–25.ISBN 978-1-85260-086-0.OCLC 22311137.

• East Coast Main Line
• West Coast Main Line
• Midland Main Line
• Highland Main Line

• BR Main Line Gradient Profiles: The Age of Steam. Hersham, UK:Ian Allan. January 2003 [1966].ISBN 0-7110-0875-2. 0301/A.
• Foster, Andrew (June 2010),A Review of the Intercity Express Programme(PDF), archived fromthe original(PDF) on 5 October 2011
• Foster, Andrew (June 2010a),A Review of the Intercity Express Programme (Annex)(PDF), archived fromthe original(PDF) on 7 November 2012
• MacDermot, E.T. (1927).History of the Great Western Railway, vol. I: 1833-1863. Paddington, UK:Great Western Railway.
• Sanderson, Joanna; Pollard, Richard; Thorne, Robert; Hradsky, Robert; Bevan, Robert; Howell, Jason; Bogdanovich, Boris; Harrison, Tim (April 2012). Meade, Susannah; Craggs, Patricia (eds.)."Great Western Main Line Route Structures Gazetteer – Prepared for Network Rail". Alan Baxter & Associates LLP.

• Pre-grouping Atlas and Gazetteer. Shepperton, UK: Ian Allan Limited. 1976.ISBN 0-7110-0320-3.
• MacDermot, E T (1931).History of the Great Western Railway, volume II 1863-1921. London, UK:Great Western Railway.

• Paddington, Reading General, Didcot and Milton (British Railways in the 1960sSectional Appendix Extract; via theInternet Archive)
• Reading, Main Line West and Bedwyn (British Railways in the 1960sSectional Appendix Extract; via theInternet Archive)