The decision means Phase 2a will open in 2027 just a year after the initial 190km phase from 1 from London to Birmingham and a junction with the West Coast Main Line (WCML) near Lichfield in 2026. In order to accelerate construction, Phase 2a works will be authorised by parliament under a separate hybrid bill.
The sections from Crewe to Manchester and the eastern branch to Sheffield and Leeds will open in 2033 and a decision on the alignment of the remaining sections of Phase 2 will be made by autumn 2016.
Revised estimates put the total cost of the 338km Y-shaped network at £55.7bn at 2015 prices.
Public consultation on Phase 2 began in 2013 and in March 2014 HS2 Ltd chairman Sir David Higgins called for the construction of the line to Crewe to be brought forward to extend the economic, capacity, and journey time benefits to the north west.
According to the government's Command Paper, High Speed Two; East and West (PDF link), which was published on November 30, Phase 2a "is a relatively straightforward section to deliver from an engineering point-of-view," with only 1.8km of tunnel, 6.5km of viaduct, and no new stations. No additional rolling stock will be required as the Phase 1 service pattern will be maintained. HS2 Ltd calculates that Phase 2a offers a benefit:cost ratio of 1.3, with additional revenue and inflation savings more than covering the cost of accelerating construction. Furthermore, the extension is forecast to generate more than £2bn in net benefits.
Crewe is already a key interchange on the WCML with services to destinations including Manchester, Liverpool, Chester, Stoke-on-Trent, Shrewsbury, and stations in Wales. However, the current layout of the station and junctions is considered to be a capacity constraint on the WCML. A new Crewe Hub station is therefore planned on the existing station site and the DfT has asked HS2 Ltd and infrastructure manager Network Rail to develop more detailed proposals on how this can be delivered.
With the completion of Phase 1 and Phase 2a, the fastest London Euston - Crewe journey times will be cut from 1h 30min via the WCML to 55 minutes, while London - Manchester Piccadilly will fall from 2h 7min to 1h 27min and London - Liverpool will be reduced from 2h 14min to 1h 46min. London - Glasgow Central will fall from 4h 31min to 3h 56min.
Construction of the London - Birmingham/Lichfield phase is set to begin in 2017 and HS2 Ltd began prequalification for the first major civil works contracts on this section at the end of September.
In addition to bringing forward the link to Crewe, HS2 Ltd has also recommended the construction of an integrated hub at Leeds, which would utilise the existing station site, while maintaining a southerly route into the city. On the western leg a terminus station is proposed alongside the existing platforms at Manchester Piccadilly.