British Prime Minister Boris Johnson on Tuesday said the UK’s high-speed railway HS2 will be built despite soaring costs, bringing faster and greener transport connections between London and northern England.

Addressing parliament, Johnson said his “cabinet has given high speed rail the green signal”.

He added: “We are going to get this done and to ensure that we do so without further blowouts to costs or schedule; we are today taking decisive action to restore discipline to the programme.”

Johnson’s full backing comes after he ordered a review into the viability of the line, the largest current infrastructure project in Europe, after years of delays and ballooning costs.

Some projections suggest HS2 could cost more than £100 billion ($129 billion, 118 billion euros), double an official 2015 estimate, and far more than was suggested when HS2 was first mooted in 2009.

HS2 will be Britain’s second high-speed rail project after HS1, the line linking London with the Channel Tunnel to France.