according the article that
@vapor trail posted, tunnels are another circumstance that Mercedes excludes. As are wet roads. And construction. or narrowing lanes.
Notably, the article stated that you
could use your phone with the system engaged (contradicting earlier posts in this thread.) The author stated he rarely went longer than 30 seconds because of all the limitations. "Mercedes has won the race to a production implementation of Level 3 driving automation, but in a sensible and unexciting way."
As I've said before, I don't think Mercedes had made any huge technological leap in abilities that other companies like Tesla haven't, and the actual use for the system is incredibly limited, but it's still at least some progress in the self-driving front.