Donning a hardhat and safety-orange coveralls, U.K. Prime Minister David Cameron joined Crossrail brass and sandhogs underground June 4 at the formal completion of tunneling work on London's $22.6-billion east-west railroad megaproject.

Starting in May 2012, eight TBMs drove 42 km of 6.2-m-dia tunnels on twin bores under central London. Another 13.5 km of station tunnels were excavated and lined with sprayed concrete. With work 65% complete on time and budget, according to Andrew Wolstenholme, CEO of Crossrail Ltd., "the challenge now shifts to … fitting out the stations and tunnels."

Crossrail is forecast to carry 200 million passengers a year after its December 2018 completion.