I think it's okay for the second or third or even tenth largest project to be called "one of the world's largest projects".

FWIW, Crossrail is on this list of the 25 "most impressive" projects - http://www.popularmechanics.com/technology/g2121/the-worlds-... .

https://en.wikipedia.org/wiki/List_of_transport_megaprojects describes it as a "megaproject", and I can agree that everything which is a megaproject is one of the largest construction projects in the world.

Looking at the list of projects which are "under construction", and ordered by cost, Crossrail is #6 at US$25B and the GBT is #10 at US$10B.

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.

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").

Longer and deeper, sure, but Crossrail is a whole other level of complexity due to being built under of one of the world's largest and most congested cities.