Concerns have been raised that enforced mandatory bicycle helmet laws appear to lead to a reduction in the number of cyclists, and increased helmet use may lead to increased risks due to the psychological effect of motor vehicle drivers being more cautious when encountering a large density of pedestrians and cyclists.
Wearing helmets may make cyclists feel safer and thus take more risks. This effect is known as risk compensation and is consistent with other road safety interventions such as seat belts and anti-lock braking systems.
In tests, adults accustomed to wearing helmets cycled faster when wearing a helmet than without, indicating a higher tolerance for risk. Tests also show that children go faster and take more risks when wearing safety gear (including helmets), and that parents allow children to be more risky when using safety gear.
Motorists may also alter their behavior toward helmeted cyclists. One small study from England found that 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).
