I wonder whether the psychological, perceptual effects on the cyclist (not the drivers) were completely controlled for.
I could imagine that the rider would ride somewhat differently, perhaps unknowingly, with and without a helmet. Especially if he were conducting a study and had a point to prove.
Donald Munro said:
Robert Chung said:
8cm = 3 inches. The size of this effect was smaller than the effect of positioning on the roadway, type of vehicle, or the gender of the rider.
Half a standard penis, although the ISO still need to standardise this unit.