Anti-helmet theory debunked

A well-publicised UK study on cyclists not wearing helmets has been debunked by researchers in Sydney.

The British study suggested that drivers overtaking a cyclist not wearing a helmet left more distance than when a cyclist had a helmet.

The two researchers from the University of NSW re-analysed the data from the study by Dr Ian Walker at the University of Bath in 2007.

Jake Olivier, from the School of Mathematics and Statistics, and Scott R. Walter, a biostatistician in injury research from Centre for Health Systems and Safety Research, Australian Institute of Health Innovation, found that Dr Walker’s theory was not sound.

The Walker study is one of the most cited by opponents of compulsory helmet laws.

Dr Walker cycled around the cities of Bath and Bristol in Britain measuring the clearance that overtaking drivers gave him while he was wearing a helmet and not wearing a helmet.  He concluded that when he was not wearing a helmet, overtaking drivers passed further away than when he had a helmet.

His theory was that drivers considered that a cyclist without a helmet was more likely to be unpredictable than a cyclist wearing a helmet and accordingly gave a helmetless cyclist more clearance.

However, Dr Olivier and Mr Walter concluded that there was little to no evidence to support Dr Walker’s theory.

They said that risk compensation theory for helmet wearing while cycling had generated increased interest in the peer-reviewed literature.

“Walker’s argument that helmet wearing affects the behaviour of motor vehicle drivers does not support risk compensation theory upon re-analysis,” they concluded.

“Helmet wearing is associated with a small difference in passing distance and is not associated with close passing.

“The evidence from this study does not justify recommendations around helmet wearing, but rather highlights the more important factors of kerb distance, road characteristics and traffic type which may inform more effective cycling safety improvements.”

Other factors were more significant – vehicle size and the cyclist’s distance from the kerb.

Big vehicles overtook more closely and the further from the kerb the rider was, the closer the motor vehicle came.

The extra distance given to those without a helmet, which Walker observed, was only when the vehicles were already well away from the bike rider, and therefore had no significant influence on the rider’s safety.

Olivier and Walker state: “Only distances greater than 2.0m are statistically significant for helmet wearing and the magnitude of the difference is 7 cm.

“Given that any evidence of a difference in passing distance related to helmet wearing is only observed for passing distances well above the recommended one metre, these results do not support the idea that any substantive risk reduction can be gained from not wearing a helmet.”

 

The full study, “Bicycle Helmet Wearing Is Not Associated with Close Motor Vehicle Passing: A Re-Analysis of Walker, 2007” can be found at:

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0075424

About Robert