The Bombardier Electrostar (sold as the ADtranz Electrostar until 2001) is a group of electric multiple unit (EMU) passenger trains manufactured by Bombardier Transportation (formerly Adtranz) at their Derby Litchurch Lane Works, in England, between 1999 and 2017. It has become the most common EMU type in Great Britain since the privatisation of British Rail, with a number of variants. Electrostar trains are most common on high-volume suburban commuter routes around London and on main line services from London to Surrey and the south coast, east to Essex, and north to Cambridge and Stansted Airport.
The model shares the same bodyshell and core structure as the Bombardier Turbostar, which is the most common post-privatisation diesel multiple unit (DMU) type; both evolved from the design by ADtranz. The Turbostar and Electrostar platforms are a modular design, sharing the same basic bodyshell and core structure, and optimised for speedy manufacture and easy maintenance. A common underframe, created by seam-welding a number of aluminium alloy extrusions, is covered by body panels and topped by a single piece roof, again made from extruded sections. Car ends (cabs) are made from glass-reinforced plastic and steel, and are bolted onto the main car bodies. Underframe components are collected in "rafts" which are bolted into slots on the underframe. The predominantly aluminium-alloy body gives light weight to help acceleration and energy efficiency.
Transport for London (TfL) announced in August 2006 that it had ordered 48 three- and four-car Electrostar trains for the new London Overground service. These were categorised by Network Rail as , and entered service in 2009 to replace the and trains on the North London Line and West London Line, and to provide the opening service on the new East London line extension in 2010.
In 2009, as part of the government's wider rolling stock plan, an order was placed for thirty four-car units intended for use by National Express East Anglia (now operated by Greater Anglia) on the Stansted Express and West Anglia services. The first of these units entered passenger service on 3 March 2011.
Production of the trains ended in 2017, when unit number 387174 for Great Western Railway was completed at Derby Litchurch Lane Works. The family was superseded by the Alstom Aventra.
The Electrostar was also selected for use on the Gautrain system in South Africa, a new railway between Johannesburg, Pretoria and Johannesburg International Airport. The trains were assembled by UCW Partnership in South Africa from components made in Derby.
c2c uses Class 357 interchangeably on all services down the London, Tilbury and Southend line from and to .
The is the backbone of Southeastern's long-distance routes, seeing services on most of its lines originating from its London termini (, , and ) including:
On the outer suburban portions of these above routes, the Class 377/5s and the support the Class 375s, but they do not work in multiple together.
The operates on the metro routes in suburban London, in conjunction with the Desiro Cities, Class 465 and Networkers, operating over the London portion of the above lines from the London termini (including ) out to and ):
This leaves the Bromley North Line, operated by (four-car Networkers). The Bromley North Line, Sheerness Line and Medway Valley Line used to be operated exclusively by the (2 car Networkers) prior to the introduction of accessibility regulations in January 2020.
Southern's fleet is found on all parts of the network, apart from the non-electrified routes. They frequent metro routes, formerly alongside the , until the latter's withdrawal in 2022, and until they transferred to South West Trains in 2014.
Often found on:
London Overground operates over four of its six lines around London:
On 8 June 2010, the route between Sandton and OR Tambo International Airport in South Africa opened in time for the 2010 FIFA World Cup. The rest between Johannesburg Park Station and Rosebank was to be completed in 2011. This section was actually opened 7 June 2012, the delay caused by work to resolve a water-seepage problem in the single-track tunnel section between Rosebank and Park. Although railways in South Africa use the Cape gauge, Gautrain is built to the more expensive standard gauge of . According to the Gautrain planning and implementation study, this is done for several reasons, including that standard gauge is safer and more comfortable to passengers. The rolling stock is also easier, quicker and less expensive to obtain than Cape Gauge rolling stock, and standard gauge is also less expensive to maintain as it is more tolerant of track imperfections than Cape Gauge. Standard gauge allows for travel at Gautrain's required speed of .
From September 2016, Great Western Railway introduced 45 four-car on peak services between and . They replaced the and the on the Thames Valley services; they now operate between London Paddington and , and . They have also since been introduced on certain services between London Paddington and .
GWR announced in 2018 that they will modify 12 units to be used on Heathrow Express due to the depot closing.
From late 2016, 29 of the Class 387/1s operating on Thameslink were displaced by the delivery of units, and were transferred to Great Northern. They operate mostly on the King's Cross-Cambridge-King's Lynn route, though they can also been seen on other services. These units were delivered in the livery of Southern, with green doors and Southern upholstery.