Today is Bike to Work Day — an event that's all about trying to get more people to ride bicycles more regularly.

If you don't feel like wearing a helmet while biking, that's fine

And here's some advice that might help with that goal: Stop forcing people to wear bike helmets.

For most bikers, this advice is anathema. The importance of wearing a helmet has been drilled into everyone since childhood. And, it's true that, as study after study has shown, you're better off with a helmet if you're in an accident.

But in the world's most popular biking cities, particularly in Europe, very few bikers wear helmets. And there are good reasons for that: biking, it turns out, isn't an especially dangerous form of transportation in terms of head trauma. And the benefits of helmets may be overstated. While they do protect your head during accidents, there's some evidence that helmets make it more likely you'll get in an accident in the first place.

Most importantly, requiring helmets deters many normal people from biking in the first place — in Australia, bike commuting rates plummeted when mandatory helmet laws went into effect. And, when there are fewer bikes on the road overall, biking becomes more dangerous.

Of course, if people want to wear helmets they are more than welcome to.

But we should think of helmets as an optional accessory, rather than an absolute requirement — and laws that would mandate all cyclists wear helmets, like one proposed in Maryland last year, are a very bad idea.

Walking and driving are just as dangerous as biking — but they don't require helmets

One question to start with is why we require helmets for bikers but not for pedestrians or drivers. Is there something inherently dangerous about biking?

It doesn't appear so. Back in the early 1990s, Australia collected good data on head injuries for walking, biking, and driving. (This was before the country imposed mandatory helmet laws for bikers.) And what they found was that biking was only slightly more dangerous than walking or driving:

Obviously, Australia is not the United States, but the two countries have very similar rates of walking, driving, and cycling.

Here's more recent data, which covers all of Great Britain from 2008 through 2012. It doesn't distinguish between different causes of death, but again shows that your odds of being killed on a bike or on foot are very similar.

Similar data has come out of France, the Netherlands, Denmark, and elsewhere.

Again, analyzing US data is tough — no one keeps track of how many miles are biked or walked in the country annually, so it's hard to convert raw numbers of injuries and deaths into meaningful rates. But on a per trip basis, biking causes more deaths than driving and just slightly more than walking.

In 2012, 1.8 percent of all traffic-related deaths were bicyclists, and 14 percent were pedestrians. Because biking makes up about one percent of all trips taken in the US, and walking about 10.9 percent, both led to a disproportionate number of deaths, compared to cars — but were relatively similar, compared to each other.

Bicycling, in reality, isn't as inherently dangerous as people often think.

Helmets don't reduce total cycling head injury rates

Helmet proponents are right about one thing: If you're in a serious accident, then wearing a helmet makes the odds of a head injury significantly lower — by somewhere between 15 and 40 percent. (This is why ER doctors and brain surgeons are so pro-helmet — they've seen firsthand what happens in helmet-less accidents.)

The data on whether helmets reduce total accidents is ambiguous

But this is only a part of the story — that data is only looking at the tiny sliver of bicycle trips that end in the hospital.

A more relevant question is how the use of helmets affects the total rate of head injuries and the overall accident rate.

Surprisingly, the data here is pretty ambiguous. Some analyses show the Australia law reduced overall head injury rates, but others find the opposite.

A recent study of 66,716 Canadian cyclists under the age of 18 looked at head injury rates in provinces with mandatory helmet laws and compared them to provinces without. The result? Head injury rates have fallen in both over the last 20 years.

Head-injury rates did drop slightly more in the helmet-law provinces, but the researchers' model found that the difference could be entirely explained by unrelated factors — things like bike lanes and other improvements to the cycling infrastructure, along with bicycle safety campaigns.

Head injury rates in provinces with mandatory helmet laws (left) and without (right)

Though US data is scarcer, it's hard to see the positive overall impact of helmets in the United States either. Between 1995 and 2002, for instance, the number of bike-related concussions suffered by people under 18 declined, but the number of young people who were biking actually dropped much more significantly.

Other data shows that despite increased voluntary helmet use by adults in the US and Great Britain, the overall number of cyclist fatalities hasn't been affected.

On the whole, when large numbers of people begin wearing helmets, we really don't see a benefit in the head injury or fatality rates. How is this possible?

It's possible that wearing a helmet could make accidents more likely

There are two reasons to think that a helmet-wearing cyclist is inherently more accident-prone one.

One can be blamed on drivers: perhaps for subconscious reasons, they seem to be less careful around helmeted cyclists.

In a 2007 study, British researcher Ian Walker rode 200 miles in the cities of Salisbury and Bristol with a sensor strapped to his bike that measured the distance of a total of 2,259 cars that passed him. He wore a helmet about half the time — and found that when he wore it, the cars came about 3.35 inches closer, on average, when passing.

The frequency of dangerously-close passes was also much higher when he was wearing the helmet — and the two times he was actually hit during the experiment both came when his helmet was on.

Many people also suggest that wearing a helmet makes cyclists themselves less cautious in their riding, increasing the chance of an accident.

drivers seem to be less cautious around helmeted bikers

This is unproven, and it's a difficult topic to research. Comparing real-world accident rates for helmeted and non-helmeted riders risks conflating all sorts of other factors (a rider's skill, for starters), and trying to do a controlled study in which you force some cyclists to not wear a piece of protective equipment raises ethical issues.

But even if each of these effects just increased the odds of an accident slightly, it wouldn't take much for that to wipe out the modest benefit of having a helmet on during that accident.

More importantly, though, there's a bigger problem with requiring all cyclists to wear helmets, whether through laws or peer pressure.

Requiring helmets sends the wrong message and discourages biking

There's a more fundamental issue: requiring people to wear bike helmets deters people from biking in the first place.

Biking to work in Australia declined after the advent of helmet laws

Case in point: Between 1986 and 1996, most states in Australia rolled out helmet laws and began fining cyclist who weren't wearing them. As a result, the percentage of people who biked to work went from 1.68 to 1.24 percent — a decline of over a quarter.

Moreover, these states implemented the laws at slightly different times, and by looking at data from the 1991 and 1996 censuses, you can see the effect of the laws even more clearly.

Bicycle Helmet Research Foundation

In red states (where laws were in place by 1991), cycling dropped significantly between 1986 and 1991. In blue states (where laws went into place between 1991 and 1996), biking dropped during that same period. (The higher two lines show biking in Australia's larger capital cities, and the two lower lines in smaller cities and rural areas, but the trends are essentially the same.)

So what's the problem with taking bikers off the road? It makes biking dramatically more dangerous, easily eclipsing the safety benefit of helmets.

It's been proven over and over again that the most important predictor of a city or region's level of safety for bikers is the number of bikers on the road.

Here's data from 68 cities in California showing the strong correlation between safety and the number of cyclists:

Injury Prevention, Jacobsen

Here's a comparison of the US and different European counties:

European Cyclists' Federation

True, it's hard to disentangle cause and effect here. These cities and countries could be safe because there are more bikers, or there could be more bikers because infrastructure and other factors make biking in them safe. But either way, it's clear that helmets do not play a major role in ensuring overall biker safety.

That's because in most the countries on the far right of the graph, helmet use is dramatically lower than in the US.

helmet laws make biking more dangerous by taking bikers off the road

This doesn't mean that if all American bikers leave their helmets at home, New York is going to suddenly turn into Copenhagen. But it does mean that safety officials' emphasis on helmets is totally misplaced — and that required helmet laws mainly make biking more dangerous by taking bikers off the road.

All this is borne out in cost-benefit analyses conducted in places that did enact bike helmet laws.

In Australia, several different researchers have studied mandatory helmet laws — looking at the lives saved by helmets, the fact that biking is now more dangerous because there are fewer bikes on the road, the actual costs of buying helmets and enforcing the laws, and the massive health costs of having fewer people biking in a country that's battling obesity — and concluded they do more harm than good.

So should I wear a helmet when I bike?

If you prefer wearing a helmet, go ahead.

But this is an argument for why you shouldn't feel guilty if you don't feel like wearing one. And it's an even stronger argument for opposing mandatory helmet laws, like the one proposed in Maryland last year.

Let's stop thinking of helmets as a critical protection against the risky activity of biking. Let's start thinking of biking as a normal, safe activity, like walking — and helmets as an optional accessory for people who are really into it.

Personal note: I'm a daily bike commuter and a long-distance tourer, and suffered an accident a few years ago in which my helmet was dented — though it's hard to say whether it "saved my life." I've lately begun wearing a helmet less, and despite the cold stares from other cyclists, am feeling better and better about it.