The effect of (mandatory) bicycle helmets on bicycle use is not clear. Several international studies show that bicycle use decreases after helmets are made mandatory, even though most studies do not find such an effect or only find a temporary effect [35] [42] [43]. These international studies have probably little bearing on the expected effect in the Netherlands, since, people use bicycles differently here. Cyclists often find helmets uncomfortable and impractical (see the question Why do cyclists choose not to wear bicycle helmets?). Making bicycle helmets mandatory could, therefore, make cycling less popular. This would be an unwelcome development from the perspective of public health (apart from crash involvement), the environment and urban traffic flow.
There are two international review studies of the effect of mandatory helmets on the use of bicycles, both dating from 2018 [35] [42]. The first study [35] shows that the research results are not unequivocal. The researcher states that mandatory helmet use could indeed result in a decrease of the number of cyclists, but that this need not always be the case and that, if the number of cyclists initially decreases, that need not be of long duration. The second study [42] is a mostly qualitative analysis of the literature. Based on their findings, the researchers conclude that there is little to no evidence of a substantial decrease of bicycle use due to the introduction of mandatory helmets. They have examined 23 studies/data sets and conclude that 2 of these studies support the hypothesis that mandatory helmets lead to a decrease of cycling, whereas 13 studies do not, and 8 studies show mixed results.
The abovementioned review studies only concern research done abroad, in particular in Australia and North America. The results probably have little bearing on the expected effect in the Netherlands. Moreover, the only Dutch study on this subject, a study among children aged 6 to 8, did not find any indications of an effect of bicycle helmets on bicycle use [11].