Hacker News Reader

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.

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

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.

Which would make it an even more fun roller coaster!