Glad your getting out there into the traffic OP. Just to add to the stories, which have been very interesting, I live in Colorado where cycling is done by many, so I have not had too many issues in the last 17 years riding in traffic. But when I lived in the Dallas/Fort Worth area, I got hit from behind. AND I was on the shoulder!! The key as others have pointed out is visibility, and your ability to see what's happening behind you so great that you have the mirror. I also run a tail light that is super bright in the daytime.