Mandatory Helmet Laws Are Like Mandatory Seatbelt Laws

I was hoping to avoid comment on Senator Liu’s mandatory bike helmet law. It is a zombie idea that pops up every so often in the US. The California legislature last considered the idea in the early 1990’s. That was during the height of bike helmet hysteria, and even then Legislators thought it was a bad idea. Two decades later, the idea has even less traction now that we can look at the experience of nearly a dozen places that tried it. Senator Liu has yet to explain why it would work in California when it failed miserably in Canada, Spain, Australia, New Zealand, and Seattle.

One argument frequently heard is that mandatory helmet laws are just like mandatory seatbelt laws. There is actually a lot of validity to that argument: Both are feel-good measures and yet counter-productive for safety.

Now you are probably thinking that seatbelt laws have saved tens of thousands of lives. You are also thinking that automobile fatalities have been on a long decline, and that seatbelts are largely responsible. You may also have watched slow-motion videos of crash-test dummies. But the inconvenient truth is that while seatbelts are good to have in an accident, there is no evidence that mandatory seatbelt laws improved safety:

That figure comes from work done by Dr. John Adams. It covered 80% of the world’s car population at the time of publication. If you have not heard of the name and believe he is some crank, it is quite the opposite. Dr. Adams literally wrote the book on modern risk analysis.

Here is another figure, showing how fatalities and injuries increased when the UK passed its mandatory rear seatbelt law:

And here is what happened when Australia implemented the law. Note again how fatalities went back up:

It is worth considering why mandatory seatbelt laws have negative consequences. One reason has to do with the idea of risk compensation:

Risk compensation is a theory which suggests that people typically adjust their behavior in response to the perceived level of risk, becoming more careful where they sense greater risk and less careful if they feel more protected. Although usually small in comparison to the fundamental benefits of safety interventions, it may result in a lower net benefit than expected.  By way of example, it has been observed that motorists drove faster when wearing seatbelts and closer to the vehicle in front when the vehicles were fitted with anti-lock brakes.

A consequence of risk compensation is that motorists drive faster, causing increased risk for pedestrians and cyclists. It is a major reason why pedestrian and bicycle fatalities have not declined.

Another reason why seatbelt laws didn’t work is because they were implemented instead of making changes in the infrastructure. It is a similar problem to bike helmet laws, which legislators also prefer to implement over more costly infrastructure improvements.