People get killed riding in groups too, in fact I would not be surprised if there is no additional protection statistically. I think sometimes a group can be in increased danger because they can cause added aggro in car drivers because they're harder to pass.
For the most part, nobody WANTS to hit a cyclist. They just don't see you in time, usually because they're distracted. I assume that the ones that are likely to hit me are people texting. They're probably looking at the road once every 5 seconds, maybe 10 seconds at worst. They're going 60 MPH. That means you need to be visible/bright enough to GRAB the attention of someone who is GLANCING at the road for a half a second 10 seconds before they get to you at 60 MPH. That means you need to be OBVIOUS from 880 feet away (a bit over 1/8 mile). Curves will make things worse for visibility, but nobody's navigating curves without looking for 10 seconds.
The best thing you can do is to do everything you can to be visible. Bright clothing and a daytime-visible flashing light. I use an Axiom Pulse 60 in the back (if you're really nervous you could look at Dinotte but I think it's overkill) and some sort of flashing white up front - I just use a little Ignita on my helmet in daylight/summer. in the winter I have more serious lights up front.
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Work: the 8 hours that separates bike rides.