[bigiain]

I'd guess that at least for the new years eve 31st, there's be more staff rostered on than usual, but probably fewer then normal doing regular traffic patrol. I suspect Halloween is similar. I've got no data or evidence to back that up (and even less for Halloween, since I'm not in the US), but I'd probably choose to remove those two days as "exceptions". Filtering out other known public holidays might improve the signal to noise ratio of the data too...