You guys are really being cavalier with the term "right of way". Right of way is the legally defined right to proceed according to the traffic laws. In this case, the car had no right of way, and the biker had complete right of way. If they got in an accident, the car would be 100% at fault.
Completely separate from the right of way is "what the biker/car SHOULD have done". I have been in this situation many many times, in fact on my daily commute, I pass an intersection that is particularly dangerous for this kind of situation. Yes, the biker has a higher responsibility for his own safety because he is in more danger than the car driver, and he should act accordingly. The car driver is cutting short his legal obligation to stop and check traffic, and is the one that created this dangerous situation 100%. For my part, I always watch for turning cars in front of me, and if there's one on a side street, I often move over to that side of the lane to make sure I become visible to them (so in this analogy, the 4oclock position). This is the same as when someone in the oncoming lane is waiting to turn left across mine and I'm behind someone, I move to the 8oclock position so that they can see that I'm behind the car. There are sometimes other cicumstances that make me not want to remain very long in the 4oclock position, so I move back to wherever I want to be and I am careful to watch the turning car, expecting him to not see me.
Now the OP says th biker was behind a car. Unless this was a truck, panel van, or some other large vehicle that has heavily tinted windows, or no windows, the driver should be able to see through the car a little bit and see the biker behind him. And before you go saying "oh that is too much to expect of a cager, that's unreasonable..." I look through cars all the time when I'm turning specifically because I understand the danger of this situation, and I have many times seen something "through" the first car and waited. This is 100% the legal responsibility of the turning car.
Yeah, the rider was careless (by elevated riders' standards) and could have prevented the close call. But assigning any legal or otherwise blame to him is a little like blaming the victim of a theft because they forgot to lock their door. Yeah it was irresponsible, but the open door didn't force someone to come in and steal their stuff.
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