the consortium, Bombardier Transportation would design, build and maintain new trains for these lines. 190 trains would be built by Bombardier at Derby Litchurch Lane Works - 40 trains for the Circle and Hammersmith & City lines, 78 trains for the District line, and 72 trains for the Metropolitan line. All the trains would be built to the same design, saving on parts and maintenance costs for Metronet. The only difference would be the length of the train, given different platform lengths on different lines. The first train was planned to enter service on the Metropolitan line by 2009, with all trains in service by 2015. In December 2006, Metronet and London Underground unveiled the completed design, with air-conditioning and walk through carriages for the first time on the Underground. London Underground also announced that 40 additional cars had been ordered from Metronet/Bombardier at a cost of £105 million. This would allow for a seventh carriage on Circle and Hammersmith & City line trains, unifying the fleet with the District line trains. In July 2007, Metronet, the private consortium responsible for the infrastructure for the sub-surfaces lines, collapsed due to financial difficulties. Following negotiations with Bombardier to allow for continued delivery of 2009 Stock and S Stock trains, TfL took ownership of Metronet in May 2008. A mockup of the train was shown off to the public in September 2008, with testing of the trains prior to delivery taking place at Old Dalby Test Track in Leicestershire from March 2009. This prevented the need for weekend or evening closures of lines in London to test trains. The first train was delivered to London Underground in October 2009. Built at Bombardier's Derby Litchurch Lane Works, trains were constructed at a rate of six a week at the height of production. In 2015, TfL ordered an additional S8 train as part of the Croxley Rail Link at a cost of £15.5million, taking the total ordered to 192. The final set was delivered 10 November 2016. The extension to the Metropolitan line was cancelled in 2017. Metropolitan line S8 Stock was initially tested overnight between and 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