With a variety of construction spread across some 350 sites, bridge builders have recently made their mark on the U.K.'s 140-mile HS2 London-Birmingham high-speed railroad. While it has had some individual success, the whole $50-billion megaproject risks going awry.
In its recent annual review, the government's Infrastructure and Projects Authority rated HS2's current chances of successful delivery as "unachievable." That was a downgrade on last year's assessment when success seemed feasible but challenging.