I think it is the same criteria you apply as a human. If you need to get into a lane and make a turn, you will slow down, block your lane and inch in till someone lets you in.

I do think there has to be an aggressiveness level in making maneuvers for an autonomous car. It doesn't mean its unsafe, it just means it could be MORE safe if the time penalty isn't big (a decision that regular drivers have a hard time evaluating since we don't measure our own maneuvers' safety accurately)