visibility option use a strobe rear light, even in day
another option for the curvy section:
I did a test commute last month (16 mi one way) and one stretch was through a curvy section of road, no shoulder. It seemed like cars were passing awfully close or maybe they did not see me until they were closer. It was daylight and clear.
So.... I stopped on a side street and turned on my rear light in strobe mode (it's a DiNotte) and what do you know, cars passed more courteously and slowly.
So you could try a good strobe light when you are on more dangerous sections of rode.