I have been going downhill at about 50 mph(long, steep hill, which i earned because i climbed it first). The speed limit is 40 mph, i was in the right hand side of the right lane, almost riding on the white line. People were still passing me, and very rapidly. I can see two reasons: First, people do not want to be beaten by a bicycle. Secondly, I think that most people, as has been mentioned before, do not want to be responsible if the cyclist wipes out.