Motorists may also alter their behavior toward helmeted cyclists. One study by Walker in England found that 2,500 vehicles passed a helmeted cyclist with measurably less clearance (8.5 cm) than that given to the same cyclist unhelmeted (out of an average total passing distance of 1.2 to 1.3 metres).[38][39] The significance of these differences has been re-analysed by Olivier,[40] who argued that the effect on safety was not significant since the passing distances were over 1 metre,[41] and again by Walker, who disagreed with Olivier's conclusion.[39]