Great Western main line

Great Western Main Line
Maidenhead Railway Bridge carrying the line over the River Thames.
Overview
Type	Commuter rail, Higher-speed rail
System	National Rail
Status	Operational
Locale	Greater London South East England South West England
Termini	London Paddington Bristol Temple Meads
Stations	25
Operation
Opened	30 June 1841 (complete line)
Owner	Network Rail
Operator(s)	Great Western Railway Heathrow Connect Heathrow Express Chiltern Railways CrossCountry South West Trains
Depot(s)	Reading TMD Old Oak Common TMD
Rolling stock	Class 43 "HST" Class 57 Class 150 "Sprinter" Class 153 "Super Sprinter" Class 158 "Express Sprinter" Class 159 "South Western Turbo" Class 165 "Networker Turbo" Class 166 "Networker Turbo Express" Class 180 "Adelante" Class 220 "Voyager" Class 221 "Super Voyager" Class 332 Class 360 "Desiro" Class 387 "Electrostar"
Technical
Line length	119 mi (192 km)
Number of tracks	Four (London to Didcot) Two (Didcot to Bristol)
Track gauge	1,435 mm (4 ft 8 1⁄2 in)
Old gauge	7 ft 1⁄4 in (2,140 mm)
Electrification	Mk3b, Series 1 and UK Master Series 25kV 50hz AC OLE (Paddington to Airport Junction) (West Drayton to Temple Meads by 2016)
Operating speed	125 mph (201 km/h) maximum
Route map ()

The Great Western Main Line is a main line railway in Great Britain, that runs westwards from London's Paddington station to Bristol Temple Meads. It was the original route of the pre-1948 Great Western Railway which was merged into the Western Region of British Railways and is now a part of the national rail system managed by Network Rail.

The line is currently being electrified. It was electrified from Paddington to Heathrow Airport in the late 1990s. Work to electrify the remainder of the route started in 2011 with an initial aim to complete the work all the way to Bristol by 2016. The programme however has been deferred for six years with no end completion forecast because costs have tripled. The four sections that are delayed are: Oxford to Didcot Parkway, Bristol Parkway to Bristol Temple Meads, Bath Spa to Bristol Temple Meads and the Thames Valley branches to Henley and Windsor.

The line was built by the Great Western Railway and engineered by Isambard Kingdom Brunel as a dual track line using a wider 7 ft (2,134 mm) broad gauge and was opened in stages between 1838 and 1840. The alignment was so level and straight it was nicknamed ‘Brunel’s Billiard Table’. It was supplemented with a third rail for dual gauge operation allowing standard gauge 4 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 to Reading (October 1861), Reading to Didcot (December 1856), Didcot to Swindon (February 1872), Swindon to Thingley Junction, Chippenham (June 1874), Thingley Junction to Bathampton (March 1875), Bathampton to Bristol (June 1874), Bristol station area (May 1854). The broad gauge remained in use until 1892. Evidence of the original broad gauge can still be seen at many places where bridges are a wider than usual, or where tracks are ten feet apart instead of the usual six.