S8 Stock

The S Stock is a fleet of sub-surface rolling stock used on the London Underground. Delivered by Bombardier Transportation in Derby, the S Stock replaced the A Stock on the Metropolitan Line. This stock has many differences from the S7 Stock, one being the seating arrangement and another being number of cars. Both types have air-conditioning and low floors to ease accessibility for disabled people, and it is possible for a passenger to walk from one car to the next while the train is moving with the new gangways between carriages, unlike older sub-surface stock.

Passenger service began on the Metropolitan Line in July 2010 and completely replaced the A Stock in September 2012.

The S designation stands for Sub-surface, following the London Underground tradition of designating surface stock with a letter associated with its intended route - A Stock on the Metropolitan Line to Amersham.

Part of Bombardier's Movia family, the stock consists of 58 eight-car trains for the Metropolitan line. S8 Stock entered service between 2010 and 2012, operating all services by September 2012.

The stock has faster acceleration than the previous A Stock although its top speed is 62 mph, 8 mph slower than A Stock but faster than C and D Stocks. During the period of dual operation with both A Stocks and S Stocks, the stock had its performance capped to match that of the older trains in order to comply with signalling constraints and avoid bunching of the service. S8 Stock seats 306 passengers compared with 448 for A stock although it can accommodate 1,226 standing passengers compare to 976 and even has dedicated space for wheelchairs.

Eventually the voltage will be increased from normal 630 volts to 750 volts. This will allow the stock to perform better and also increase power demands of air-conditioned, fully-motored-axle trains, and allow the trains to return energy to the network through regenerative braking.

At present the stock is operated manually, but London Underground will hopefully activate automatic train operation once the necessary signalling is in place by 2018.

Features:

The S stock is air-conditioned throughout: the sub-surface tunnels (unlike deep-level tube lines) allow the exhausted hot air to disperse, and two-thirds of the sub-surface network is in the open air. The stock has regenerative brakes, returning around 20% of their energy to the network and thus increasing energy efficiency.

End external displays show two lines of text: the top line for the destination, and the bottom for the line. Internally, it has a larger dot matrix indicators (DMIs) than D Stock (C Stock lacks DMIs, as did A Stock). The DMIs show destination and line, and can display other messages such as safety notices. There are also DMIs on the exterior, with text alternating between destination and line, and on the S8 stock the type of service, i.e fast, semi-fast or all stations.

Another new feature is that to prevent accidental pressing of emergency alarms there are flaps over the alarm buttons where the wheelchair spaces are.

Air-conditioning is a first on any London Underground train is by Mitsubishi and has two circuits so that if one fails there is still 50% capacity. Through gangways from car to car are another innovation, as the London Overground's Class 378 also has the same feature.

Passengers can now move from crowded cars to one with more room without having to get off at the next station and board another car. This provides extra room for standing and creates a sense of security.

 CCTV enables the driver to see into every car, while track-to-train video links give the driver a view of the train exterior before leaving a station.

There is a fold-out set of steps in each driver's cab to allow fast evacuation in an emergency, all trains on the London Underground have this feature.

The stock has cantilevered seating for easy cleaning and accessible storage of bags. S8 Stock has a mix of transverse and longitude seating with four wheelchair spaces per train. S8 Stock trains are 133.68m.

The stock is the first on the Metropolitan line with DMIs and automated voice announcements. It uses the same announcer voice as 2009 stock on the Victoria line and C Stock on the Circle, District and Hammersmith & City lines.

All stock can operate on all sub-surface lines, with selective door operation used at stations that are shorter than the train.

S8 Stock may operate as a seven-car S8-1 formation.

Entry into service:

S8 was initially tested overnight between Amersham and Watford via the Watford North Curve from 9 November 2009. Driver training began in early January 2010, and the first train entered revenue service on 31 July 2010, shuttling between Wembley Park and Watford.

By 27 June 2011, S8 Stock was running along the whole Metropolitan line. Deliveries were suspended by Transport for London in November 2011 due to concerns over reliability. A number of trains were delivered to London Underground's Neasden depot, but were not accepted to enter service. Deliveries resumed in mid-December 2011.

In August 2012, London Underground confirmed that strap handles would be introduced on S8 Stock, in response to passenger complaints over the height of the handrails as compared with the old A Stock.

All 58 S8 trains had been delivered to Neasden Depot by 15 September 2012. 11 days later the A Stock trains were completely withdrawn. It was reported that 37 of the new trains would be sent back to Bombardier for urgent modification and drivers were unhappy with the driver's cabs.