South East Main Line

South Eastern main line
The line crossing the River Thames over Hungerford Bridge
Overview
Type	Commuter rail, heavy rail
System	National Rail
Status	Operational
Locale	Greater London South East England
Termini	London Charing Cross London Cannon Street Dover Priory
Operation
Opened	1842–44 in stages
Owner	Network Rail
Operator(s)	Southeastern
Rolling stock	Class 375 "Electrostar" Class 376 "Electrostar" Class 395 "Javelin" Class 465 "Networker" Class 466 "Networker"
Technical
Number of tracks	5 (across Hungerford Bridge ) 4 (Charing Cross to Borough Market) 2 (Borough Market to London Bridge) 12 (London Bridge to Bermondsey split including Brighton lines) 5 to 6 (Bermondsey split to New Cross) 4 (New Cross to Orpington) 2 (Orpington - Dover)
Track gauge	1,435 mm (4 ft 8 1⁄2 in) standard gauge
Electrification	750 V DC third rail 25 kV 50 Hz AC OHLE (Ashford International)

A detailed diagram of the line can be
found at South Eastern Main Line diagram

The South Eastern main line is a major long-distance railway route in South East England, UK, one of the two main routes crossing the county of Kent, going via Sevenoaks, Tonbridge, Ashford and Folkestone to Dover. The other route is the Chatham main line which runs along the north Kent coast to Ramsgate and Dover via Chatham.

The line was built by the South Eastern Railway (SER), which was in competition with the London, Chatham and Dover Railway (LCDR), hence the duplication of routes in Kent.

The original main line was given sanction by Act of Parliament in 1836. The route first authorised was from London Bridge via Oxted, Tunbridge,Maidstone, Ashford and Folkestone. The route was to make use of the existing London and Croydon Railway and London and Greenwich Railway companies tracks. The SER was not a company that had a large amount of capital to spare. As a cost-cutting measure, authorisation was secured in 1837 to make the junction with the London and Croydon Railway at Norwood, Surrey. instead of at Corbett's Lane. However, the London and Brighton Railway were authorised to build from Norwood southwards in 1847. It was suggested by Parliament that further savings could be made by avoiding having lines running in parallel valleys for 12 miles (19 km) if the SER were to make its junction further south. The London and Brighton were to construct the line, and the SER were to purchase it at cost on completion. Both companies would operate trains over the route. The London and Brighton took advantage of this to ensure that gradients would be kept as shallow as possible, even at the expense of substantial earthworks and a mile-long tunnel at Merstham. The SER main line diverged from the London and Brighton's line at Reigate Junction, which the London and Brighton opened to traffic on 12 July 1841.