Those seeking to improve the situation of bicyclists, PARTICULARLY through laws or regulations, should first consider the possibility of unintended consequences…
Helmets protect rider’s heads. Bicycle riders sometimes suffer head injuries. So it would go without saying that mandatory helmet laws would improve cyclist safety, right? Well,maybe not when substitution effects (or other human nature effects) are factored in. Mandatory helmet laws have the unintended consequence of suppressing cycling. Effects of Bicycle Helmet Laws on Children’s Injuries — by Pinka Chatterji, Sara Markowitz found children cyclist’s head injuries are down, and so are other injuries, and so is the amount of cycling; from the abstract:
we find helmet laws are associated with reductions in bicycle-related head injuries among children. However, laws also are associated with decreases in non-head cycling injuries, as well as increases in head injuries from other wheeled sports. Thus, the observed reduction in bicycle-related head injuries may be due to reductions in bicycle riding induced by the laws
More broadly, people behave differently when they are helmeted; people (drivers) around cyclists behave differently depending on whether or not the cyclist is helmeted. These are human nature effects and very hard to quantify, but exist nonetheless. Risk homeostasis affects both riders and drivers.