I can't recall the study, but there is also a correlation of behavior in the US where car drivers give cyclists without helmets more room.<p>Anecdote: It was about 1994 and I was riding my bike in the bike lane along Santa Teresa Blvd to the southeast. A VW Beetle got within 4" of my rear tire and honked their horn trying to cause me to crash and run me over. I was wearing a helmet but that wouldn't make any safety difference. I probably should've not worn a helmet to seem more like a human.