Systems with even a few elements can be remarkably complex. On the face of it using a helmet while biking seems like a good idea, but it turns out helmet use discourages biking and makes it seem dangerous. When something is seen as dangerous, few people participate. People who get exercise are healthier than those who don't and policies that encourage exercise can be preventative and cost effective. Denmark and the Netherlands both partially promote bicycling to lower healthcare costs even to the point of partly funding cycling infrastructure with saved healthcare monies.
Helmet use seems sensible as blows to the head can be devastating. But it turns out mandatory helmet use kills participate in bike sharing programs and also makes the activity seem more dangerous that it is. Some have done the statistics of auto and bike head injuries and a case can be made for mandating helmets while driving cars - particularly for those under 25 and those over 70. But, of course,s that will never happen.
Helmet use in many biking countries is rare yet the injury and fatality rates are much lower than in the US. There are a variety of reasons for this - traffic calming, a larger percentage of cyclists implies a lower percentage of a risk taking population, driver training, and frequently separate cycling lanes among them. (John Pucher of Rutgers has written extensively on this - Making Cycling Irresistible is a good overview paper.)
It is strange that cities and suburbs refuse to adopt traffic calming policies. Even when cycling isn't considered, slowing traffic can greatly increase safety and lower the cost of auto accidents. It is also enormously effective in lowering child injury and death. In Europe 30 kph (19 mph) speed limits are common in cities and suburbs and 20 kph (12 mph) exist in some areas. In the US 25 mph limits are considered low.
A real problem is it is difficult for people to imagine change and probably even more difficult for institutions. It is unfortunate as much safer transportation systems are possible - assuming you have the imagination to analyze the components together rather than separately.