The U.K.'s London to Birmingham high-speed railroad project, HS2, is meeting its flexible construction schedule but faces significant pressure on its $46.5-billion target cost set at 2019 prices, according to the government's latest assessment.

With nearly 30,000 workers spread across the project, contractors have opened 350 sites along the route, shifted more than 31 million cu yd of earth and launched five tunnel boring machines (TBMs). 

Opening the line into north London "remains on track to be delivered between 2030 and 2034," says Mark Harper, the government’s transportation secretary.

However, without finding savings, project owner HS2 Ltd. is projecting around a $2.2 billion cost overrun, $230 million more than it estimated in March. 

Lower than planned productivity on civil contracts accounts for nearly 60% of the potential overrun. So far, HS2 Ltd. has drawn $1.7 billion of its $6.5-billion contingency for the project.

Construction of about 125 miles of line by four large international joint ventures began just over two years ago. Project contractors will deploy 10 TBMs to bore the line’s 64 miles of tunnels.

So far, the project company has spent $21 billion on construction and awarded contracts for work not yet started, valued at $12.2 billion. The Skanska Costain STRABAG joint venture has just launched its second TBM in London, following the first last month.

“Construction continues to gather pace, and the launch of the [program's] fifth tunnel boring another significant moment," said Mike Lyons, HS2 civil delivery director, in a statement.