Fifth Carriage for London Overground services

"Shprdbush-overground-2011" by Senseiich - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons.

London Overground will have a 25% extra capacity by upgrading the trains from four to five cars as part of £320 million investment program.

From TFL's press release

Passengers on the London Overground network are set for more comfortable journeys as the first five-carriage train, which will increase passenger capacity by 25%, took to the rails today. An extra carriage is being introduced to London Overground trains to meet increasing demand for the highly popular rail service - providing more comfortable journeys and room for an extra 170 passengers per train.

The increase from four to five-carriage trains is part of Transport for London's (TfL) £320m programme to boost capacity on the London Overground network. The rollout of the longer trains will start on the East London Line followed by the North and West London lines and be completed by the end of 2015.  

London Overground will also be able to carry more passengers on the Gospel Oak to Barking route once the line is electrified, and its diesel trains are replaced with electric ones, by 2018. Passenger capacity on the Watford to Euston line will be increased when the power supply is upgraded.  

Under TfL, London Overground has become one of the most popular and punctual railways anywhere in the country. It has brought previously under-used parts of the urban network back into full use, while services have been radically improved with continuing investment and expansion to parts of the capital once not well served by rail.  

Local business groups have hailed the transformative effects of the London Overground, with Ben Davies, Founder of Independent Shoreditch Business Alliance and the Ministry of Startups, saying:  'Many of the entrepreneurs and their teams at the Ministry of Startups use London Overground to get into work. As we're based half way between Shoreditch station and Liverpool Street, it is an essential transport link.

'The start-up businesses in Shoreditch really value London Overground and were delighted to hear about the forthcoming increase in capacity. It will make a significant difference to both staff and visitors and improve the passenger experience. Many people in London only use the Tube network, we think they're unaware of how regular London Overground services are. We love it!'  

From 31 May, TfL will look after three quarters of all journeys in and out of Liverpool Street station - having integrated West Anglia and Liverpool Street to Shenfield rail services into the TfL network.

The West Anglia services will join the London Overground Network, and the Liverpool Street to Shenfield services will be run by TfL as the first phase of the introduction of TfL-run Crossrail. 

To accommodate the longer five-car trains a programme of infrastructure upgrades has been required.

These include:

• Construction of a new train stabling facilities at Silwood, south east London and also in Wembley;
• Reconfiguration of the existing maintenance depots at New Cross Gate and Willesden;
• Platform extensions at London Overground stations across the network and associated signalling/power works.

 Source