Potential effects of mandatory wearing of bicycle helmets

נשלח 4 בפבר׳ 2011, 3:39 על ידי Sustainability Org   [ עודכן 4 בפבר׳ 2011, 3:57 ]

Potential effects of mandatory wearing of bicycle helmets. The effect on the number of injuries amongst cyclists of mandatory wearing of bicycle helmets is determined by three different partial effects, or mechanisms, which can pull in different directions. The three partial effects are the helmet effect, the behavioural effect and the exposure effect. The effect of mandatory wearing of bicycle helmets on the number of cyclists injured can be modelled as the product of the three partial effects.

The helmet effect is the protective effect of bicycle helmets, i.e. less severe injuries in the case of accidents. The size of this effect depends mainly on two factors: (1) What type of cyclists are using a helmet, and (2) to what degree the use of bicycle helmet increases.

The behavioural effect is the effect of wearing a helmet on the cyclist's risk of being involved in accidents. A cyclist who uses a helmet is more protected against injury than a cyclist who does not use a helmet. It has been suggested that this can lead to cyclists with helmets cycling less carefully (faster, paying less attention, in more difficult conditions, children being allowed to cycle on their own more than before etc) than cyclists without helmets (Bjørnskau, 1994B). If mandatory use of helmets leads to less careful behaviour amongst cyclists, this may lead to cyclists being involved in more accidents per kilometre cycled than before (the behavioural effect). Such an effect can totally or partially offset the protective effect of more cyclists using helmets.

The exposure effect is the effect of mandatory wearing of helmets on the amount of cycling. Mandatory use of bicycle helmets has been found to make cycling less attractive, so that the amount of cycling is reduced. Reduced cycling may reduce the total number of injured cyclists, but is likely to increase the accident and injury rate among cyclists (Erke and Elvik, 2007).

The effects on the number of injured cyclists of mandatory wearing of bicycle helmets, and of campaigns for the use of helmets, have been evaluated by:

Wood and Milne, 1988 (Australia)

Vulcan, Cameron and Watson, 1992 (Australia)

Cameron, Vulcan, Finch and Newstead, 1994 (Australia)

Scuffham and Langley, 1994 (New Zealand)

Robinson, 1996 (Australia)

On the basis of the studies, best estimates of the effect of mandatory wearing of bicycle helmets on the number of cyclists injured are given in table 4.10.2.

Table 4.10.2: Effects on injuries of mandatory wearing of bicycle helmets.

 

Percentage change in the number of injuries

Injury severity

Types of injuries affected

Best estimate

95% confidence 
interval

Increased use of helmets

Head injuries

-25

(-30; -19)

Increased risk per km cycled

All injuries

+14

(+10; +17)

Less cycling

All injuries

-29

(-30; -28)

Net effect

All injuries

-22

(-23; -21)

 

In total, mandatory wearing of bicycle helmets seems to have reduced the number of head injuries amongst cyclists by around 22%. The results are likely to be affected by publication bias, time trends and methodological weaknesses that have not been controlled for. Another problem with the results is that no clear relationship can be found between the degree to which the use of bicycle helmets increased and the effect on injuries that has been found. If mandatory wearing of bicycle helmets had caused the reductions of injuries that have been found in the studies one would expect larger increases of helmet wearing to result in larger injury reductions. Since no such relationship has been found, it is doubtful if the injury reductions actually have been due to mandatory wearing of bicycle helmets.

Four studies have discussed the effects of the introduction of mandatory wearing of bicycle helmets in New Zealand (Povey, Frith and Graham, 1999; Robinson, 2001; Scuffham and Langley, 1997; Scuffham et al., 2000). The analyses show the importance of controlling for long-term time trends in the number of injured cyclists. Robinson (2001) concludes that the injury reductions that have been found in many studies are a result of time trends, and not effects of the bicycle helmet law.

Source: Handbook of Road Safety Measures (Emerald Insight 2009 ISBN 978-1-84855-250-0)


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