[elcapitan]

It would be fun to see an "agile" tunnel project.

"This rock is too solid to drill through with our machines!" – "Ok, for now let's just drill around it and make it an underground rollercoaster instead of a railway, we can get back to the original design later!"

[crzwdjk]

This actually happened in St. Petersburg, when they ran into difficulties tunneling under the river on Line 2. They ended up going under the difficult section, and now there's a 6% downgrade on that section of the line, which is pretty much a rollercoaster by subway train standards.

[tonyedgecombe]

That's not agile, that's a pivot :)

[Annatar]

Not in this case, as the train is specified to go at 250 km/h, which means that the tunnel had to be pretty straight, or else the train might derail at that speed.

[ucaetano]

Which would make it an even more fun roller coaster!