The new Stratford Market Depot was completed in March 1998 - allowing for testing and commissioning of the new 1996 Stock trains, as well as the testing of the new extension itself. Following this, the first phase of the line opened on 14 May 1999, the second on 24 September, and the third on 20 November. Westminster, complicated by the interface with the subsurface platforms, which remained in operation, opened on 22 December 1999, shortly before the Millennium Dome deadline. By February 1999, however, the cost of the extension had gone up to a total of £3.3 billion.