I'll agree with Tony here. The key while riding in groups is no overlapping of wheels. It's just the sane thing to do especially if some of the people with whom you are riding have a difficult time riding a straight line and/or are sketchy riders in other ways.
I have to comment, however, that as far as encounters with cars and trucks go, there are extreme differences in how cyclists are treated in different countries. I've ridden throughout the U.S., Canada, and Europe and in some countries (e.g., Italy, France) I've found drivers to be more than tolerant of sharing the roads with cyclists. In others (e.g., many parts of the U.S.) they would just as soon hit you regardless of whether to are riding single file on a broad shoulder or hugging the curb. A friend of mine was just hit and left for dead last week by the driver of a pick-up truck that fled the scene and has yet to be apprehended. He is currently in critical condition with 8 broken ribs, 3 broken vertebra, a collapsed lung and internal damage so sever he has had to have over 1/3 of his large intestine removed. And all this occurred while he was riding on a quiet road with a should that was almost 15 feet wide.
