Our Sunday ride leader always, always stresses safety before each ride. At the beginning of April a cyclist was descending a steep hill when a pickup truck made a left turn in front of him, resulting in his death. We are encouraged to have a flashing strobe light on the front (as well as the back) whenever we ride, day or night. This reminded me of an article I read years ago, and thanks to my search engine, I found one which makes the same point.
If you don't care to read this (but it is enlightening), I'll give you the short version: unless we train our brains to recognize cyclists, it takes longer to "see" them, sometimes never seeing them. In the article I remember, the point was the brain will interpret a cyclist as a tree or stop sign because we are more vertical than say, a car. Of course, our brains are trained but it isn't us who we are worried about.
Therefore it is incumbent on us, the cyclists, to do whatever we can to make ourselves visible: bright colors, hand (full hand, please) and arm horizontal movements, reflective clothing, and flashing lights are some of the things that come to mind. Being respectful of traffic lights and stop signs are another.
Your actions have consequences. For instance, running a stop sign might trigger a negative reaction in a vehicle, who might react against the next cyclist he sees. Give a good example ALL the time.
Years ago, when I was training for my coast-to-coast trip, part of my Sunday ride included Bee Cave Road. Those familiar with the area know that with the wind behind you, going down the hill toward Weston Lane can generate 40 mph or more (still less than the vehicle speed limit). On such a morning I approached Weston in excess of 35 mph when a pickup left the stop sign in front of me. I braked and did a hard right but unfortunately rolled my tire off the rim and went down hard. I had my Camelbak to break the fall but still it took a few minutes before I could move. While laying in the middle of Weston Lane I saw the pickup continue east. I guess his conscience got the better of him, in that he circled back around to check on me. Nothing broken, only a few scrapes, thanks to the Camelbak and my helmet. Oh yeah, the driver was a cyclist on his way to his Sunday ride.
My other vehicle accident involved a pickup that rolled a stop sign. I had the right of way, saw him and saw him slow to the stop sign. Unfortunately, I was obstructed by his windshield post, and he didn't come to a complete stop and accelerated. His left front fender connected with my front wheel. Again, Camelbak and helmet saved the body. He did have to replace my front wheel.
Be safe. Be alert. Do what you can to be seen. And remember, it doesn't do you any good to be dead right.