The trouble with scientific assessments of bike helmet safety is that it's impossible to compare apples to apples, because wearing a helmet changes the accident. For instance, some studies show that cyclists who wear helmets ride less cautiously than those with their heads free. Other studies have shown that drivers drive closer to helmet-wearing cyclists than they do bare-headed bikers.
But what if you could turn back the clock on a real bike accident, and check to see whether wearing a helmet would have protected the rider? That's exactly what three researchers did at the KTH Royal Institute of Technology in Sweden.
Madelen Fahlstedt, Peter Halldin, and Svein Kleiven used computer modeling to simulate what the effect of a helmet would have been on existing injuries. First, they conducted simulations of the real accidents' effects on the cyclists' heads without a helmet, and compared these to actual scans of the victims' brains. This allowed them to match up the bleeding patterns and check that their model was good. The researchers reconstructed three accidents for the study.
Then they ran the simulations again, this time with helmets in place. The result? Helmets reduced the risk of concussion by 54%, and "drastically cut the risk of skull fractures."
"We can see how much the brain tissue is stretched in the collisions," said neuronics researcher Madelen Fahlstedt, "and that the tissue is stretched most in those areas where the impact occurred." In the simulated crashes, a regular bike helmet reduced the stretch rate of brain tissue by between 33% to 43%.
The reduction in the risk of skull fracture is even bigger. "We saw a great reduction of stress on the bones, as a result of wearing a bike helmet, from 80 megapascals down to 10 megapascals," said Fahlstedt. "This figure indicates how much load you put on a given surface, and, translated into more understandable terms, this means a reduction from 100% risk of skull fracture down to 10% for those wearing helmets."
But like every bike-helmet safety study, this doesn't tell the whole story. It's pretty clear by now that wearing a bike helmet reduces damage significantly, if you have an accident and hit your head. But day-to-day cycling really isn't that dangerous. If you're a mountain biker, then you probably want to pop a lid on your melon, but if you're riding to the shops or commuting to the office, the risk is pretty low.
After all, if we wore a helmet for every situation where it would help in case of head impact, we should be wearing them when we ride in a car—almost certainly the most dangerous thing most of us do every day—and that seems pretty ridiculous.