What the actual rules are matter far less than that traffic is predictable. Like in Boston it's typical for a few cars to get into the intersection to take a left, traffic goes around them in both directions and only on the change to red to they go. Not technically legal but normal. 4-way stops where nobody stops and everyone times their roll unless there's a reason to. Also not technically legal but normal. Nobody with an opinion worth caring about complains about these things. Blowing lights many seconds after they've changed is still wild IMO.