[twic]

Gotthard base tunnel: 4 million man hours http://edition.cnn.com/2011/WORLD/europe/11/23/gotthard.base...

Crossrail: 20 million man hours three years ago http://m.londonlovesbusiness.com/business-news/london-transp...

I'd love to see some more reliable figures, though.

[m-i-l]

Crossrail is at 100 million working hours so far, with 10,000 people working across over 40 construction sites, according to http://www.crossrail.co.uk/news/crossrail-in-numbers (which also describes it as "Europe's largest construction project").