In California, parents are not legally required to vaccinate their kids. They are, however, required to make their kids wear bike helmets. How did we get into a situation where biking was seen as a greater risk than polio and the measles?

California passed its youth bike helmet law in 1994. It was one of the first states to do so, and led to dozens of other states passing similar legislation. California State Senator Carol Liu now wants to extend the “benefits” of mandatory helmet legislation to adults.

But what evidence is there that mandatory helmet legislation is effective? In doing a literature search, I find hardly any studies that looked at the effectiveness of California’s 1994 law. But the raw data is available online to do your own analysis.

The EPICenter online injury database tracks hospital admissions for injuries, with fields for age, race, location, and cause of injury. This is one of the databases used by helmet promoters to justify helmet laws. I pulled numbers from the database, and did time-series graphs. I encourage others to also review the data.

Before getting into the results, let me offer the usual caveats. The data only go back as far as 1991. And the data do not directly measure cycling activity levels (i.e. a decline in injury numbers could be a result of less cycling). Also keep in mind that hospital data records are notoriously unreliable. Despite those limitations, one would expect to see dramatic reductions in head injury numbers given the supposed 80% effectiveness of bike helmets.

So here is the total number of bicycle-related traumatic brain injuries (TBI) in the California database, for ages 0-17:

The vertical line indicates when the state law went into effect. At first glance, the post-legislation TBI level does seem slightly lower. But was the post-legislation decline a result of the helmet mandate, or merely a continuation of an ongoing trend?

To help answer that question, let’s compare against reported pedestrian accidents, shown in the following time-series graph. It is interesting that the youth pedestrian TBI rate saw a similar rate of decline — even though there is no pedestrian helmet mandate. This suggests the decline in cycling head injuries was mainly due to fewer kids walking and biking, and not a result of the helmet mandate.

Finally, let’s next look at the bicycle TBI data for the adolescents, ages 14-17. The reason for doing this is that adolescents are more similar to 18+ riders in the type of cycling and amount of adult supervision. As can be seen, the helmet mandate was ineffective for adolescents as TBI injuries were unchanged relative to pre-legislation levels. If the helmet mandate is ineffective for adolescents, it is unlikely that it would suddenly start to work when they turn 18.

Conclusion

When the California Legislature passed the youth helmet law in 1994, it did so on the basis of speculative and dubious studies by helmet promoters. But now that the state has had more than 10 years of real-world data, it is clear the helmet experiment has been an epic fail. There no clear evidence the law reduced injuries, and it diverted millions of dollars in resources that could have been spent on more effective measures. The Legislature must not repeat this mistake with Senator Liu’s adult helmet bill.

If anything, the Legislature should rescind the youth helmet requirement. The parent-child relationship is sacrosanct. In free countries, government does not interfere in that relationship except in extraordinary cases. The decision about wearing bicycle headgear isn’t one of them.