British Rail Class 377

The Class 377 Electrostar is an electric multiple unit type built by Bombardier Transportation (previously ADtranz) at their Derby Works, from 2001 to present. The Electrostar family, which also includes Classes 357, 375, 376, and 378, is the most numerous type of EMU built in the post-privatisation period of Britain's railways. They have become the de facto flagship of the Southern fleet.

Description
The units are found working suburban services in south London, and rural commuter services to Sussex, Kent and the South Coast, on which they replaced the old 4Cig and 4Vep slam-door stock. Although built in the early 2000s, the new units had a troubled introduction: being fully air-conditioned, their higher power consumption compared to the slam-door Mark 1-based stock that they replaced led to major upgrades being required to the 750V DC third-rail power supply used in the Southern region. The collapse of Railtrack following the Hatfield accident further delayed this upgrade work and the new stock did not enter squadron service until 2003.

Class 377s are fitted with external CCTV cameras for driver-only operation. There is a disabled seating area, and both the intermediate coaches have toilets. Bodyside power doors are electrically operated, a move away from the air powered systems of previous generation EMUs. Dual voltage units are fitted with a Brecknell Willis high speed pantograph, which incorporates a pair of aerofoils on the pan knuckle to steady the pan head against the OLE contact wire. The configuration of a 377/5 unit is:
 * DMCO(A) - 2 motors on inner bogie, sander, auxiliary converter module
 * MSO - 2 motors on inner bogie, standard toilet
 * PTSO - pantograph, transformer, compressor, disabled toilet
 * DMCO(B) - 2 motors on inner bogie, sander, auxiliary converter module

Mitrac
Mitrac is the Bombardier Train Management System (TMS). It provides monitoring of on-train systems, fault finding diagnostics, event monitoring and preventative maintenance. In conjunction with the onboard GPS receiver, Mitrac controls Selective Door Operation (SDO), as well as automatic Passenger Information System (PIS) displays and Public Address announcements. Engineers can access the system remotely via GSM to download the fault log, then carry out real time diagnostics and maintenance whilst the train continues in service.

Couplers
The Class 377 uses Dellner couplers instead of the Tightlock type originally used on Southern's Class 375s. Southern's 375s were all converted to Class 377 when their Tightlock couplers became redundant after the retirement of the "slam-door" stock such as the Class 421. These reclassified units can still be identified due to their blue, grey, and red seating, as opposed to the green seating fitted to Southern's native 377s. They can also be identified by having a cluster of two main lights at each side of the cab, as opposed to the Southern 375s' three main lights, including a separate red lamp. Note that Southeastern's 375s (sub-classes 375/3, 375/6, and 375/7) were converted to Dellner couplers but not reclassified; their 375/8 and 375/9 units were fitted with Dellner couplers as built.

Traction current supply
All units can receive power via third-rail pick-up which provides 750 V DC. There are eight pick-up shoes per unit (twice the number of previous generation 4 car Electric multiple units), and this enables them to ride smoothly over most third rail gaps. The shoe mechanism is air-operated, so that when the train switches to AC traction current they are raised out of the way. Some of the units in the 377/2 and 377/5 sub-classes are dual-voltage, and are fitted with a pantograph to pick up 25 kV AC from overhead lines. This is used on the West Coast Main Line between Milton Keynes and East Croydon. Since March 2009 dual-voltage Class 377 sets have also been operating some Thameslink Bedford to Brighton, Gillingham and Ashford services. (see below).

Among the remaining units, the trailer carriage in each unit has a recess in its roof where a pantograph could be fitted, to allow for future conversion to overhead AC power. Despite most units being DC-only, the class is numbered in the 3xx series normally used for AC units.

Additional units and the Thameslink Programme
In April 2007, as part of the Route Utilisation Strategy for the Brighton Main Line, it was announced that Southern would obtain an additional 48 Class 377 carriages to replace an identical number of Class 319 carriages (12 4-car units) that were due to be transferred to First Capital Connect. Further to this, eleven more dual-voltage units were added to the order, making a total of 23. They were ordered from Bombardier in March 2008 and were delivered in First's corporate colour scheme but with Southern spec interior (green seats). The units were commissioned at Southern's Selhurst depot in South London before being transferred to First Capital Connect's Bedford Cauldwell depot. The first of these, unit 377501, was delivered to Cauldwell depot on 27 February 2009 after making its first appearance through the Thameslink Central London core. The 377/5s operate mainly on the Bedford to Brighton services but in the peaks form part of FCC's and Southeastern's new joint service to places such as Gillingham and Ashford. Once FCC's new NeXt Generation Electrical Multple Units (NXEMU's) come into service, the 377/5 fleet will be returned to Southern.

Delays in the construction of the Class 377/5s for First Capital Connect saw the temporary transfer of eight of Southern's Class 377/2s to FCC to enable them to implement the planned timetable changes on 22 March 2009; the loss of these units until September 2009 was covered by the temporary cascade of a number of Class 350/1s to Southern from London Midland, which operated services between East Croydon and Milton Keynes.

The NXEMUs will be fitted with ATO (automatic train operation) for use in the Thameslink corridor between Kentish Town and Blackfriars. ATO is a computerised system that controls the traction package (motors and brakes) to drive the train automatically. Because a very intense service is planned, ATO can provide a much shorter headway between trains than conventional lineside signalling. When using ATO the driver is only required to oversee opening and closing the doors, and then tell the computer that the train is ready to start. Should the need arise the train can still be driven manually.

Southern

 * Brighton Main Line: Brighton – Gatwick Airport - London (various destinations)
 * East Coastway (Brighton – Eastbourne/Ore)
 * West Coastway (Brighton – Portsmouth/Southampton & Littlehampton - London)
 * Redhill - Tonbridge (Tonbridge to Redhill, Victoria, London Bridge or Charing Cross)
 * West London Line (East Croydon – Milton Keynes Central)
 * Sutton & Mole Valley Line (Horsham, Guildford & Epsom Downs to London)
 * Caterham & Tattenham Corner branches (selected workings)

First Capital Connect

 * Thameslink: (Brighton-Gatwick Airport-London-Luton-Bedford also Bedford to Ashford/Gillingham in peak hours)