Wolves in Yellowstone are not exactly rare, but they do tend to stay away from roads, at least to a greater degree than bears, who will sometimes stick close to roads (especially females, as it serves to protect their cubs from boars). But seeing a wolf pack cross the road like this is much more rare - so much so that the earlier in the year, when another driver through Yellowstone had a similar encounter, it went viral.
Also, let's all just sit and enjoy the fact that these lovely tourists were respectful of our Park and its wildlife. They didn't try to take a selfy, get out of the car and approach, nor did they chase after them on motorcycles.
Great job, tourists! You're welcome back anytime!
See the whole video below!