It is "essential for the UK" that HS2, which will link the Midlands with London and the north, goes ahead says an MPs' report.
The House of Commons Transport Committee's report also says the risks of not going ahead with the project "significantly outweigh the risks of doing so."
The committee, chaired by Labour MP Louise Ellman, also said serious thought should be given to building the second-phase of the line - which will run to the north from the East Midlands - at the same time as the first phase London-to-Birmingham stretch is being built.
The report also calls on the Department for Transport to emphasise that the estimated cost for HS2 is £28 billion, not £50 billion, due to contingency costs.
The first phase of the scheme, from London through the Chilterns to Birmingham, is due for completion in 2026.