In The 85% solution I discussed the absurdly optimistic predictions in injury preventions, and why there is no hope of their ever being met. But there is another problem: there is no one consistent definition of injury.
How injured is injured?
It has to be one of everybody’s worst fears: a brain injury which leaves you a vegetable. Liddites love to talk about these – right before telling you that helmets prevent 88% of brain injuries. Just think for a minute: is it credible that a couple of centimetres of polystyrene foam could prevent a concussion? well, yes, it is. Is it credible that it could prevent brain injury sufficient to cause permanent intellectual disablement or death? Problematic.
Problematic for two reasons: first, the way helmets work: the foam crushes until it can crush no more. A large impact will rapidly reach that point, after which no further energy is absorbed. Indeed, the foam may fracture, in which case the helmet will have absorbed much less energy than designed – polystyrene foam absorbs little energy in brittle fracture. You can verify this for yourself with a bit of packing some time. It has been stated by Britain’s leading helmet tester that the energies car v. cyclists collisions routinely exceed the capacity of Formula 1 racing helmets.
Second, and more controversially, it is now thought that the dominant cause of serious traumatic brain injury is something called diffuse axonal injury, caused by rapid twisting of the head causing the two lobes of the brain to be torn apart. These rotational injuries have been documented in car crash victims (who form the bulk of seriously brain injured people). The worst injuries come from side impacts. That’s why side curtain airbags are now becoming common.
To separate this from the emotive issue of helmets, try thinking instead of the polystyrene foam packaging traditionally used for electronic goods. What is it good for? It’s there to prevent damage due to bad handling in transit, there is no way you would expect it to protect your new TV if it was hit by a truck. So why do people continue to insist that cycle helmets “saved their life” when hit by a truck? It’s a logical disconnect.
So helmet laws fail because the injuries which cause concern are of a type and severity which helmets cannot prevent.
< The 85% solution | How injured is injured?
