Obviously correlation doesn't mean causation, but if there really is something about that line of work that lowers risk, I wonder what it is. Is it simply using your brain more often than the average person, or is it something specific to navigating and planning out routes, or maybe it's something to do with constant recall of the same streets and locations? Or maybe it has nothing to do with any of that, and it's more to do with the type of people who become taxi drivers.