The tricky science — and trickier politics — behind helmets

Michelle Sipics Features, Issue 2 1 Comment

The crash took less than five seconds. One moment I was riding along, half a block from the end of my commute. The next, a red SUV hit me with its passenger-side mirror. I wobbled, crashed and landed, hard, in the eastbound lane of Market Street. My head hit the pavement, knocking me out for a few seconds. I was still dazed when I came to. I remember that someone moved my bike. The SUV’s driver kept trying to lift me by my bleeding left arm.

It could have been much worse. I ended up with a lot of road rash and tendon damage. Still, the car following behind hadn’t run me over after I crashed. I hadn’t split my skull open when my head smacked against the asphalt. Mostly, I felt grateful for my helmet.

Cyclists tend to have strong opinions on helmets. Personal experience influences some, while others consider issues of convenience or would prefer to improve safety in different ways. It’s easy to find riders who say they will never ride without a helmet. It’s just as easy to find those who think helmets are a waste of time. But for all the debate, there isn’t much discussion of how helmets are supposed to work, and how to determine whether they really do. Without that knowledge, the dialogue around helmets is missing a critical part of the picture.

Crash-Test Dummies

I walked away from my own crash confident that my helmet had saved me from the hospital or worse. I hit my head hard enough to be knocked out. Without the helmet, there could have been some real, lasting damage. Right?

The truth is, there’s no way to know what would have happened if I hadn’t worn a helmet. I can’t prove that I would have suffered a head injury. Unlikely as it may seem, it’s possible that I could have been in the same crash without a helmet and still walked away all right.

This uncertainty is what fuels most of the skepticism toward the effectiveness of bike helmets. Real-life crash data doesn’t have a control group for comparison. There was no “control” me riding to work by the same route, hit by the same SUV, with all other circumstances the same except the helmet.

“There isn’t a peer-reviewed paper where helmeted versus unhelmeted impacts have been studied to show how effective helmets were,” says Peter Cripton, a professor of mechanical engineering at the University of British Columbia. It’s easy to understand why: Scientists can’t ethically expose cyclists to the risks from a crash to find out whether helmets work, even if they could somehow set up helmeted and unhelmeted crashes that were otherwise exactly the same.

In the absence of helmet-less doppelgängers for every reported crash, researchers who have studied bike helmets to date have mostly used epidemiological data.

That means they take data from thousands of crashes and see how many riders were wearing helmets versus how many weren’t. Then they determine whether wearing a helmet correlates with a reduction in head injuries. By and large, that’s what the studies suggest.

“We focus on the facts, and we believe in the scientific evidence we see,” says Eric Richter, brand development manager for bikewear company Giro Sport Design. “Helmets have been shown in reputable studies to reduce the most common head injuries associated with cycling by 45 to 85 percent, and we believe they’re one of the most effective ways you can reduce your chances of being injured in the event of a crash.”

“Nobody expects to get hit in the head. But incidents happen, and if they do, you just have to think of the consequences.”

To see the whole picture, it’s important to understand how a helmet is supposed to work. Despite decades of adjustments by manufacturers for comfort and aerodynamics, helmets work in a fundamentally simple way: They reduce the acceleration your head experiences when you whack it against something. Cripton, whose research group at the University of British Columbia focuses on reducing the impact of human injury, compares them to car airbags.

“In a crash, you hit your head on the airbag and the airbag deforms,” Cripton says. “The airbag is like a pillow and helps you to ride down the acceleration and reduce the potential that you’re going to have a skull fracture and a brain injury. That’s exactly how a helmet works.”

The outside of the helmet is a hard shell. The inside layer, made of polystyrene, is where the airbag-like effect occurs. “When you hit your head hard,” Cripton explains, “this layer compresses on impact and absorbs the energy needed to be absorbed so that you don’t get a skull fracture.”

Helmet certification tests are designed to measure this effect. A helmet is put on a head-like form, which is then dropped onto a hard surface (an anvil, essentially). The helmet’s ability to manage the energy of the impact is tested by measuring acceleration. In the U.S., for the helmet to pass and be sold, the measured acceleration of the impact must be less than 300 g. This is the same “g” — a unit of gravity — that we reference when we talk about astronauts experiencing “zero g.”

It may surprise you to learn that helmets are certified based on a simple drop test. When we think about crashes, most of us picture a collision while riding or skidding out and sliding along the road. But most crashes involve a fall to the pavement.

Consider just how easy it is to injure yourself by falling sideways while sitting still. “When we’re sitting on a bicycle, 1.5 to 2.0 meters is about the height our head is at, depending on the size of the rider,” Cripton says. “Just falling off our bikes not wearing a helmet, if we hit our head, there’s a very high probability — it’s near 100 percent — of skull fracture and brain injury, and that goes down to less than 10 percent if we just wear a helmet.”

Cripton recently published the first peer-reviewed study comparing helmeted and unhelmeted impacts, using heads from crash-test dummies. He and his colleagues used the same methodology as helmet certification tests: dropping head-forms from certain heights onto anvils and measuring the acceleration on the head when a helmet was worn, then again without a helmet. Cripton was quick to note that each helmet was only used for one drop and then replaced, just as recommended for helmets that have undergone a crash.

The results were clear. Wearing a helmet significantly reduced the acceleration experienced by the dummy heads, which translates to a significant reduction in injury risk. Even at a drop height of only half a meter, based on Cripton’s calculations, an unhelmeted rider would have a 16 percent probability of a severe brain injury.1 With a helmet, the risk fell to less than 1 percent.

At and above the more realistic drop height of 1.5 meters, the risk of serious brain injury without wearing a helmet was nearly 100 percent. Ultimately, the researchers concluded, bicycle helmets “changed the probability of severe brain injury from very likely to highly unlikely.”

This isn’t to say that helmets are a one-step fix for cycling safety. Past certain heights and speeds, even helmeted riders have a high likelihood of trauma with a head impact (though in Cripton’s study, the risk is always higher for unhelmeted riders). Plenty of cycling injuries involve something other than hitting your head. A helmet won’t protect against road rash or a broken arm. The most common cycling injuries vary based on location and the infrastructure available to riders. Arm fractures are universally common, and no one would claim a helmet helps prevent them. Still, if you do hit your head — or are involved in a collision with a motor vehicle, which statistically increases the risk of severe head injury — well, that’s the type of common cycling injury helmets were designed to address.

“Nobody expects to get hit in the head,” Cripton says. “But accidents happen, or incidents happen, and if they do, you just have to think of the consequences.”

The Choices We Make

Widespread helmet use is a fairly recent phenomenon. Anyone who has watched a professional cycling race is familiar with the sea of bobbing helmets, but these only became a requirement after the death of unhelmeted rider Andrei Kivilev, who suffered a skull fracture following a collision in the 2003 Paris-Nice race. (In a press release following Kivilev’s death, the International Cycling Union noted that its proposal for mandatory helmets more than a decade earlier had been “rejected by a large majority of professional riders.”)

Outside of professional racing, helmet use varies widely but has grown in recent years. In its 2014 report, the Bicycle Coalition of Greater Philadelphia noted that among the cyclists it observed, 55 percent wore helmets — an increase of 95 percent since 2005.

Toni Saarela, a life sciences researcher, falls within that 55 percent. Saarela, who has been cycling since childhood and calls it one of his preferred forms of transportation, says he almost always wears a helmet.

“Why not?” he asks. “That’s really the reason. Close calls happen relatively often when biking among cars or in the bike lane. Of course you have to be careful, but sometimes it’s out of your hands, and then the helmet might come in handy.”

“Ultimately I believe that the best way to prevent bike commute accidents is not to make bikers more crash-proof, but to make cities more bike friendly.”

Saarela has also experienced a crash. Quite the opposite of my out-of-nowhere incident, he describes it like this: “You’re on your bike observing the thing unfold — your front wheel getting crushed under a car, in this case — realizing there’s nothing you can do to stop it.” A car ahead of him, traveling in the bike lane, had stopped. Its driver backed into him.

“I fell off my bike and rolled out of the way, and the car didn’t hit me,” Saarela says. “I wasn’t hurt. I took the bike to the shop and was riding again the next day.” Saarela points out that he didn’t hit his head in this particular crash.

Matt, a 43-year-old scientist who declined to give his last name to protect his privacy, has been cycling regularly for about 20 years. Around half that time was spent cross-country mountain biking. He says he would never ride a mountain bike without a helmet, but doesn’t wear one for his daily commute in Philadelphia.

“I know there are many pros and cons,” Matt says. “But ultimately I believe that the best way to prevent bike commute accidents is not to make bikers more crash-proof, but to make cities, currently built around and for cars, more bike and pedestrian friendly. This means slowing down traffic and sharing the road.”

Matt notes that he’s had several crashes cycling in the city, ranging from incidents with trolley tracks to collisions with other cyclists. He says he has never been injured.

“A helmet gives me a false sense of safety, and it also induces a bias in car drivers’ perception, as they see me as less fragile,” he says.

Legal Matters

Matt’s argument falls in line with those of many cycling organizations who say that requiring a helmet discourages people from riding bikes. Instead, these advocates say that governments should focus on making infrastructure safer for cyclists in the first place.

In one recent example, Carol Liu of the California State Senate introduced a bill to require adult cyclists in her state to wear helmets. In announcing the bill, Liu said the law would “help protect more people and make sure all riders benefit from the head protection that a helmet provides.” Dave Snyder, executive director of the California Bicycle Coalition, was quick to disagree.

“It’s inarguable that a helmet will protect your head in the event of a crash,” Snyder says. “They are at least partially effective. They might be very effective. But the point we are making is that a law that mandates helmet wearing will result in fewer people riding a bike. It will discourage the important safety improvements that must be made to really protect people, and that socially, the act of riding a bike will be more dangerous for those of us who are still riding.”

John Boyle, research director for the Bicycle Coalition of Greater Philadelphia, says his organization would also oppose such a law if one were on the table here.

“We strongly encourage people who ride bicycles to wear a helmet every time they ride,” Boyle says. “But we also believe that mandatory helmet laws would have a negative effect on bicycling.” (The helmet requirement in Liu’s bill was dropped in early April, according to advocacy website Streetsblog. Instead, the legislation now calls for the California Office of Traffic Safety to conduct a “comprehensive study of bicycle helmet use.”)

“Of course you have to be careful, but sometimes it’s out of your hands, and then the helmet might come in handy.”

Boyle notes that several studies have shown helmet laws discourage cycling. One of the most frequently cited studies, published in The BMJ in 2006, reviewed cycling data from multiple jurisdictions around the world that had introduced helmet legislation. Studying locations where comprehensive cycling data was collected both before and after the implementation of these laws, author D.L. Robinson found that while helmet use increased, the number of people cycling went down.

“Before and after data show enforced helmet laws discourage cycling but produce no obvious response in percentage of head injuries,” Robinson wrote in the study’s summary. “This contradiction may be due to risk compensation, incorrect helmet wearing, reduced safety in numbers, or incorrect adjustment for confounders in case-control studies.”

“Helmet laws are an attempt to address safety,” Boyle says. “But they’re not very good at doing that. Not as well as improving infrastructure, which is one of the key things to making bicycling safer, and also having more bicycles on the road.”

Interestingly, the Bicycle Coalition’s report also notes that streets with better bicycle lanes saw more helmet use.

Where does that leave a cyclist who just wants to get safely from point A to point B? Helmets work, but requiring them might discourage cycling. They significantly reduce the chances of severe brain injury if you hit your head, but can’t protect against all the possible injuries associated with crashes. Is it smarter to forget about helmets and focus on better cycling infrastructure for everyone?

Maybe the easier question is whether anything could actually change someone’s mind about wearing a helmet.

“I don’t know,” Matt says. “Maybe if my wife gave me an ultimatum.” ◆


Comments 1

  1. I know plenty of cyclists who have had accidents where no car was even involved. So, the argument of improving the infrastructure isn’t the be all, end all. If there’s science that shows helmets can help reduce major trauma, then why not just wear the dang thing? Ok, so a helmet may not be trendy or it messes up your new hairdo, but it’s simply common sense! Better safe than sorry.

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