[Mawr]

It is not possible for me to see you in your car with any sort of reliability; even if I could the benefits are dubious and again, unreliable.

Looking at your car is all I need anyway - I can tell if you've seen me by your behavior, you're either slowing down to yield to me or you're not. If you're not, the only possible outcome of knowing you're seeing me is being misled into stepping into your path of travel.

[Brian_K_White]

It's not all or nothing. A hundred different things all add up and none of them do the entire job, nor are entirely unnecessary simply because they don't do the entire job.