Major European contractors have flocked to London for a piece of the 21-kilometer Crossrail tunnel project now advancing at more than 40 sites across the city. Billed as Europe's largest infrastructure project, Crossrail survived the U.K.'s toughest austerity drive in generations, in part because officials pushed back its schedule by a year. That move cut the estimated cost by around $1.6 billion, to $23 billion.