British railway route linking London and Weymouth
 
The South West Main Line (SWML) is a 143-mile (230 km) major railway line between Waterloo station in central London and Weymouth on the south coast of England. A predominantly passenger line, it serves many commuter areas including south western suburbs of London and the conurbations based on Southampton and Bournemouth. It runs through the counties of Surrey, Hampshire and Dorset. It forms the core of the network built by the London and South Western Railway, today mostly operated by South Western Railway.
Operating speeds on much of the line are relatively high, with large stretches cleared for up to running. The line has four tracks for most of the length between Waterloo and Worting Junction near Basingstoke, from which point most of the line is double track. A couple of miles from the Waterloo terminus, the line runs briefly alongside the Brighton Main Line west branch out of London Victoria, including through Clapham Junction – the busiest station in Europe by railway traffic.
The oldest part of the line, in the London Borough of Lambeth, was used from 1994 to 2007 by Eurostar trains running out of Waterloo International.
History.
London–Southampton (1830–1848).
The first written proposal for a railway line linking London and Southampton was published on 23 October 1830 by a group chaired by the Southampton MP Abel Rous Dottin. The following February, Francis Giles was commissioned to survey the route and a formal scheme, which also included the construction of new docks on the Solent, was presented at a public meeting on 6 April 1831. Giles, who was familiar with the west Surrey and north Hampshire area, having worked as an engineer for the Basingstoke Canal, examined potential routes via Guildford and Farnham. However, his favoured alignment, via Basingstoke, was chosen to facilitate a future western branch to Bath and Bristol. His detailed survey was published on 5 December 1833 and the construction of the line from London to Southampton was approved in the London and South Western Railway Act 1834 on 25 July the following year.
Under the terms of the 1834 act, the London and Southampton Railway company was authorised to issue shares to the value of £1 million (equivalent to £ million in 2023) and to borrow a further £330,000. Around half of the money was raised from businessmen from Lancashire, with much of the remainder provided by landowners from south Hampshire. Giles had estimated that his route would take three years to build at a cost of £800,000–£900,000. A formal ceremony to mark the start of construction took place at Shapley Heath, near Winchfield, on 6 October 1834, and the contracts for the earthworks and bridges had been let by the end of that month. Giles's strategy was to use numerous small-scale, local contractors, with work taking place simultaneously on multiple sites along the route. By February 1836, just under had been finished, with a further completed by the end of August 1836. Shareholder dissatisfaction with progress led to Giles's resignation on 13 January 1837 and his replacement by Joseph Locke. 
Locke assessed the progress of the construction works and estimated that around £1.7 million (£ million in 2023) would be required to complete the line. He dismissed many of the smaller contractors, awarding much of the remaining work to Thomas Brassey. He also instituted a more rigorous supervision system by his assistant engineers. On 30 June 1837, the London and South Western Railway Deviations Act 1837 was passed, enabling the company to raise further capital and authorising deviations to the route. On 21 May 1838, the first section of the South West Main Line, between Nine Elms and Woking Common, opened with intermediate stations at Wandsworth (later replaced by Clapham Junction), Wimbledon, Kingston (now Surbiton), Ditton Marsh (now Esher), Walton and Weybridge. The extension westwards to Shapley Heath (now Winchfield), with a station at Farnborough, opened on 24 September 1838.
On 14 June 1839, the London and Southampton Railway adopted the new name of the London and South Western Railway (LSWR). Four days earlier, the first trains had run from Winchester to a temporary terminus north of Southampton at Northern Road (now Northam). The extension from Shapley Heath to Basingstoke also opened on 10 June 1839, and the section between Basingstoke and Winchester, which required three tunnels, was finished in May the following year. The opening ceremony for the completed line from Nine Elms to Southampton took place on 11 May 1840, with a directors' train leaving London at 8 am and arriving at the permanent terminus, designed by William Tite, around three hours later.
The LSWR did not intend Nine Elms to be its permanent northern terminus, and in 1844 an extension of to a new station at Waterloo Bridge was authorised. Three years later, the company acquired the Richmond and West End Railway, which had been authorised to build its own tracks alongside the London–Southampton line between Clapham Junction and Waterloo. Construction of the line north of Nine Elms, known initially as the "Metropolitan extension", began on 11 July 1848. The four-track line was carried on a viaduct of 290 arches, which followed a sinuous path to avoid encroaching on Vauxhall Gardens, the local gas works, and Lambeth Palace. The new terminus, designed by Tite and with four platforms, was initially known by a variety of names including York Road, Waterloo Bridge and Waterloo. On the day that Waterloo was opened, the Nine Elms terminus closed to passengers and was replaced by Vauxhall station.
Southampton–Brockenhurst and Hamworthy–Weymouth (1844–1857).
In February 1844, a group of Dorset businessmen, led by Charles Castleman, a solicitor from Wimbourne, proposed a railway line linking Southampton to Dorchester. Surveyed by William Moorsom, the Southampton and Dorchester Railway (S&amp;DR) was to take an indirect route to serve as many towns as possible, and its sinuous nature gave rise to the nickname "Castleman's Corkscrew". In particular the line would run via Ringwood, bypassing Bournemouth, which was a small village at the time. Poole, with a population of only 6,000, would be served by a branch from a station at Hamworthy. Castleman hoped to persuade the LSWR to operate the route, but the company refused, fearing that it would not be able to build any further lines west of Salisbury if it accepted. Instead, the Great Western Railway (GWR) agreed to run services using broad-gauge trains. Concerned at this development, the LSWR proposed a rival scheme, the Salisbury &amp; Dorsetshire Railway, which would have paralleled much of Castleman's line. Both proposals were considered by the Board of Trade, which favoured the S&amp;DR, but which also indicated that the route should be standard gauge. The LSWR agreed to lease Castleman's line for an annual sum of £20,000 (equivalent to £ million in 2023).
The Southampton and Dorchester Railway Act 1845 was granted royal assent on 21 July 1845 and, the following month, Samuel Morton Peto was contracted to build the line. Materials were shipped by sea to Poole and the first part to be completed was the section between Ringwood and Dorchester. Wet weather during the winter of 1846–1847 delayed the completion of the eastern half of the line. Difficulties encountered during the construction of Southampton Tunnel meant that the first public trains between Blechynden (close to the site of the present Southampton Central station) and Dorchester ran on 1 June 1847. The link to the LSWR opened on 29 July that year, allowing through running of trains between London and Dorset, albeit with a reversal at the Southampton terminus station. The initial timetable was five trains per day in each direction between Nine Elms and Dorchester, with the fastest services taking ;templatestyles src="Fraction/styles.css" / ;5+3⁄4 hours. The LSWR was authorised to acquire the S&amp;DR in the London and South Western and Southampton and Dorchester Railways Amalgamation Act, passed on 22 July 1848. 
The Southampton and Dorchester Railway Act 1845 gave the LSWR running rights over the southern section of the Wilts, Somerset and Weymouth Railway. The line, which was taken over by the GWR in 1850, was laid with dual-gauge track between Dorchester and Weymouth to allow both companies' trains to operate. The first trains ran over the new line on 20 January 1857, although trains to and from Weymouth could not call at the LSWR's Dorchester station without reversal.
Brockenhurst–Hamworthy (1863–1893).
The section of the South West Main Line between Christchurch and Bournemouth was built as part of the Ringwood, Christchurch and Bournemouth Railway. The company had opened the first part of its line, between Ringwood and Christchurch, on 13 November 1862, but passenger numbers were low. The proposal to continue the line to the growing seaside resort of Bournemouth was authorised by the Ringwood, Christchurch and Bournemouth Railway Act 1863. Work on the extension began in late 1865, and the single line opened 14 March 1870.
Until December 1872, Poole was served by a station on the western side of the Harbour Bridge. Through carriages to London had been introduced by the LSWR in May 1860, and the branch line had been doubled in 1863–1864. The second station to serve Poole opened on 2 December 1872 and was served at first only by Somerset and Dorset Joint Railway trains. It was constructed as part of the Poole and Bournemouth Railway, initially an independent company, but taken over by the LSWR in July 1871. The extension to Bournemouth West, including an intermediate station at Parkstone, opened on 15 June 1874.
By 1881, the population of Bournemouth had reached 17,000. The town was served by two stations, neither of which was in the town centre. The LSWR proposed a new station, adjacent to the town hall, on a new railway between the two existing facilities. Local opposition to the proposed link resulted in its route being moved northwards, and plans for the central station were abandoned. Instead, a new Bournemouth East station, designed by William Jacomb with a roof, was constructed. It opened on 20 July 1885 and the new link line was commissioned on 28 September 1886. Pokesdown station, between Christchurch and Bournemouth East, opened on 1 July 1886.
The South Western (Bournemouth &amp; c.) Act 1883, passed on 20 August 1883, authorised the construction of a cut-off line between Brockenhurst and Christchurch, which would reduce the distance between the two by around compared to the existing route via Ringwood. The works included a new Christchurch station and the doubling of the single line between Christchurch and Bournemouth East, both completed on 30 May 1886. Progress on the cut-off line was hindered by poor weather in spring 1887, which flooded cuttings and damaged embankments. The direct Brockenhurst–Christchurch line opened about a year later than planned, on 5 March 1888, with intermediate stations at Sway, New Milton and Hinton. The initial timetable was nine services per day from London to Bournemouth East, with eight in the opposite direction. The fastest trains took around three hours to cover the between the capital and Bournemouth. Portion working was instituted, allowing trains to split at Brockenhurst, with the front sections running as express services to Weymouth and the rear sections operating as local stopping trains to Bournemouth.
The Holes Bay Curve, authorised by the South Western Railway Act 1890, was constructed by Lucas and Aird and opened on 1 June 1893. The new link allowed London–Weymouth trains to bypass Ringwood, taking the shorter route via Bournemouth and Poole. Opening on the same day was the avoiding line at Branksome, which allowed trains to bypass Bournemouth West, eliminating the need for reversal.
Branchlines.
The first line to branch from the London–Southampton route was the Eastleigh–Gosport line, opened on 29 November 1841. The line was intended to serve Portsmouth, which could be reached via a floating bridge from Gosport. The station at Eastleigh, originally known as "Bishopstoke", was designed by William Tite, and had opened on 10 June 1839 with the section of line between Basingstoke and Northern Road. A further junction at the station was added with the completion of the Eastleigh–Salisbury line, which opened to freight on 27 January 1847 and to passenger trains on 1 March of the same year.
By 1850, four lines branching from the South West Main Line had opened to serve locations in west Surrey and east Berkshire. The Guildford Junction Railway, which diverged from the South West Main Line at Woking, opened on 5 May 1845 and