In my area, maybe in yours too, there is a neurological disorder that incapacitates peoples' use of turn signals. This handicaps other drives as well, inasmuch as they have to guess if the driver in question is awake, alive, off the phone, out of a trance, aware that they are in a vehicle, in this time zone, aware they are in a human body, aware that other people exist and might also be driving, aware that they are not Napoleon nor the Buddha, and so on. There is no cure for this disorder, nor does it improve with time. There are some indications that the larger the size of the vehicle being driven on a regular basis the more severe the condition becomes. The National Institutes of Health is researching this and preliminary studies defining the disease should be published by 2035.