Cycle helmets are useless, says brain surgeon - Telegraph

A controversial point-of-view to be sure. Strange theory about how far cars stay away from people with helmets and those that don't wear them. I would point out that you can fall without an automobile being involved - like wet drawbridge grates. Click title for link.

Research conducted by Dr Ian Walker, a professor of traffic psychology at the University of Bath, showed that motorists drove around 8cm closer when overtaking cyclists with helmets.
He suggested that drivers think helmeted cyclists are more sensible, predicable and experienced, so therefore the driver doesn't need to give them much space when overtaking.
Non-helmeted cyclists, especially non helmeted "women" are less predictable and experienced, according to this study and so motorists give them more room.
However, Mr Marsh's comments are likely to anger cycling safety campaigners, who believe that helmets provide essential protection on Britain's busy and narrow roads.