Photo by Richard Masoner / Cyclelicious on Flickr.

On Tuesday morning, the Environmental Matters Committee of the Maryland House of Delegates will hold a hearing on House Bill 339, to require that every person operating a bicycle in Maryland wear a helmet. This bill is bad policy.

Mandatory helmet laws cause fewer people to bicycle, and when fewer people bicycle, cycling becomes less safe. So much less safe, in fact, that decreased ridership increases the individual cyclist’s risk of injury more than wearing a helmet decreases risk of injury.

This does not mean that bicyclists should not wear helmets. We encourage bicyclists to wear helmets. However, there are several reasons why people who are deeply committed to bicyclist safety oppose mandatory helmet laws.

Mandatory helmet laws decrease ridership.

Numerous studies of places that have enacted helmet laws have shown this to be true. The most commonly-cited study—Dorothy Robinson’s “No Clear Evidence from Countries that have Enforced the Wearing of Helmets”—examined data from New Zealand, from Nova Scotia, Canada, and from several states in Australia. In each place, the mandatory helmet law significantly decreased ridership, from 20% to 44% with an average of 37.5%.

(One can debate whether Maryland can expect a decrease of this magnitude. There is no local data available, so this analysis uses the average of 37.5%. But even if the decrease is only 20%, the lowest Robinson observed, even half of that, the result is the same.)

Lower ridership makes bicycling less safe.

We are defining “safety” as the likelihood of a bike-auto crash. By saying that decreased ridership makes bicycling less safe, we mean that a decreased rate of bicycling within a population is correlated with increased crash rates, and vice versa.The leading article on this topic—Peter Jacobsen’s “Safety in Numbers: More Walkers and Bicyclists, Safer Walking and Bicycling”—reviews data on biking, walking, and injury rates in 68 California cities, 47 Danish towns, 14 European countries, and the United Kingdom.

Across the independent sets of data from these many jurisdictions, Jacobsen finds a consistent, inverse, curvilinear relationship between bicycling and injury rates, determining that “the total number of pedestrians or bicyclists struck by motorists varies with the 0.4 power of the amount of walking or bicycling respectively.” Expressed simply, more people biking leads to fewer per capita crashes while fewer people biking leads to more per capita crashes.

Jacobsen also derives a formula for how this affects the individual cyclist: “Taking into account the amount of walking and bicycling, the probability that a motorist will strike an individual person walking or bicycling declines with roughly -0.6 power of the number of persons walking or bicycling.” In other words, as more people bicycle, the per capita risk to each bicyclist of a crash decreases; if fewer people bicycle, the per capita risk to each bicyclist increases.

Helmets do not make cyclists as much safer as commonly thought.

For the individual, of course, the story is different. Wearing a helmet is likely safer than not wearing one. This is true for bicyclists; it is also true for people who are skydiving, rock climbing, sitting under an oak tree, or taking a bath. Individually, we make our decisions based on our own risk tolerances and values, and many of us choose to wear helmets and encourage our loved ones to do so.

But at the broader level, where we ought to analyze legislation and public policy, how much safer will a helmet make a person in a bike crash that leads to a head impact? This is a topic of debate and uncertainty, but as research methods improve we move further from some of the magical thinking that took hold due to early estimates—derived from emergency room data rather than population data—that suggested helmet effectiveness rates of 85% and above.

Generally, those estimates came from retrospective studies that looked at people with head injuries in emergency rooms and compared the numbers who lived and died, and whether they were wearing helmets when they were hit. When more recent studies have attempted to compile these data into meta-analyses with more informative sample sizes, their results do not approach the long-accepted 85% level. Some show a smaller effect; others, none at all. In fact, in population-level studies focusing on hospitalization rather than emergency room visits, helmets have no discernible, statistically significant effect on hospitalization rates. (Jacobsen 2012)

Recent studies that have focused on overall health, rather than simply crash mortality rates, have shown that the individual and public health benefits grossly outweigh the costs, by a factor of 20:1. (De Jong 2012)

The mandatory helmet law in Maryland will increase danger for Maryland cyclists.

Assuming that the helmet law will decrease cycling by the 37.5% average in Maryland, the total Maryland cycling population, post helmet law, would shrink to only 62.5% of the current cycling population. Assuming also that Jacobsen’s safety-in-numbers effect holds true in Maryland—as it has consistently throughout California and across Europe—the number of motorists colliding with people bicycling will increase by roughly 17.1% per capita (1-0.6250.4=0.171)

For the individual, these assumptions mean that the likelihood of injury from a crash with a motor vehicle would increase by roughly 33% (0.625-0.6=1.326)—regardless of whether the individual wears a helmet. The increased risk comes solely because mandatory helmet laws take people off bicycles, and fewer people on bicycles makes the remaining bicyclists less safe. Substantially.

Maryland does not keep much data on bicycling, but one piece of data that we do have is that in 2010, there were 734 reported bicycle crashes in Maryland. Looking only at this data—and assuming ridership decreases by 37.5% from the helmet law in Maryland—we might expect only 459 crashes instead of 734.

However, this expectation is wrong. Due to the decreasing “safety in numbers,” we would instead expect to see 537 crashes, or 78 additional crashes directly attributable to the mandatory helmet law. So even though the total number of crashes might decrease, that is not because the law has made cyclists safer; it is because substantially fewer people are riding bikes, and those that still ride are measurably less safe, because of the law.

Discouraging cycling runs counter to other Maryland priorities.

The state of Maryland has launched, or is poised to launch, two programs dedicated to encouraging cycling. The mandatory helmet law would undermine the success and safety of both.

First, knowing the overall benefits of biking to public health and well-being, transportation, economic development, and other public priorities, the state of Maryland initiated a campaign to get more people riding bikes. Maryland’s Department of Transportation introduces the campaign on their website with:

Governor O’Malley’s Cycle Maryland initiative is an effort to encourage more Marylanders to get out and ride, and to make bicycling a true transportation alternative. Cycling is a great way to connect to your community, support a cleaner environment, encourage a healthier lifestyle, reduce household transportation costs and enjoy Maryland’s magnificent landscape.

With the mandatory helmet law reducing ridership, Maryland will be left with more people to figure out how to move, and will have to treat more people for health problems associated with sedentary lifestyles.

Second, Maryland has contributed funds to expand the popular and successful Capital Bikeshare program to Montgomery County. Due to the nature of bikesharing, users are less likely to wear helmets, more likely to be casual rather than experienced users, and more likely to be operating in urban environments with motor vehicles. So perhaps the legislators proposing this mandatory helmet bill mean to ensure the safety of those riders, before bikesharing arrives in the state?

However, again, consider the data: Capital Bikeshare users have logged over 3.4 million trips, with an approximately 38% lower helmet usage rate than the general population. (Kraemer 2012) There have been zero fatalities and only one head injury. That is roughly one crash for every 88,000 miles ridden! Yet by driving potential cyclists away, a mandatory helmet policy would undermine the likelihood of success of the program in Montgomery County, Baltimore, and other areas statewide.

That safety record speaks for itself and shows that biking is not an inherently dangerous activity. Mandatory bicycle helmet laws falsely portray it as such, and in doing so create a false sense of danger that limits ridership and undermines the many positive impacts of mass cycling for Maryland.

“Contributory negligence” makes the law extra harmful.

And finally, some believe that this law is acceptable and benevolent and will not have these impacts because there is no fine for violation. But this law has other, even more dire consequences for violators.

Maryland, like the District and Virginia, is a “contributory negligence” jurisdiction. That means if the victim of a crash contributed in any way to her own injury, she can claim no civil recovery for her damages. In Maryland, violation of a law is negligence per se.

Thus, it is possible that a cyclist who rides the bus to work on a rainy morning but chooses to take a bikeshare bike home when the weather clears, and suffers permanent brain injury when a drunk driver veers into a bike lane and strikes her, could be denied any civil recovery as a result of not wearing a helmet.

Is this the transportation future we want in Maryland? Is this the sort of public policy we hope to encourage?


In Maryland, we can anticipate a mandatory helmet law to reduce bicycle ridership by 37.5% (along with its accompanying public health, environmental, and economic benefits), per capita crashes to increase by 17%, and the per capita risk of a crash to increase by 33% for every person riding a bike in the state of Maryland, regardless of whether he or she wears a helmet.

In a broader sense, these laws are a form of victim blaming—telling bicyclists that it is our responsibility to avoid the risk of injury by padding ourselves, rather than the state’s to design a transportation network capable of moving non-motorists with a decent level of safety and efficiency.

WABA opposes a mandatory helmet law in Maryland because it is bad policy based on accepted, tested, and peer-reviewed data—not just some libertarian philosophy or desire of cyclists to “feel the wind in our hair.”

Fundamentally, we do believe that the legislators proposing this mandatory helmet law hope to do what is best for bicyclist safety, but they have significantly erred in determining what will, in fact, be best. They have the power to impose new risks on each of us who rides a bike, even when we wear helmets. We hope they will consider this information seriously and decide that a mandatory helmet law is a bad policy for the state of Maryland.


De Jong, Piet. 2012. The Health Impact of Mandatory Bicycle Helmet Laws. Risk Analysis. 5 (32): 782-790.

Jacobsen, Peter L. 2003. Safety in Numbers: More Walkers and Bicyclists, Safer Walking and Bicycling. Injury Prevention 9 (3): 205-209.

Jacobsen, Peter L. and Harry Rutter. “Cycling Safety” City Cycling. Ed. John Pucher, Ed. Ralph Buehler. Cambridge: MIT Press, 2012. 141-156.

Kraemer, John D., Jason S. Roffenbender, and Laura Anderko. 2012. Helmet Wearing Among Users of a Public Bicycle-Sharing Program in the District of Columbia and Comparable Riders on Personal Bicycles. American Journal of Public Health 102 (8): e23-e25.

Robinson, Dorothy L. 1996. No Clear Evidence from Countries that Have Enforced the Wearing of Helmets. British Medical Journal 332 (7543): 722-725.

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Shane Farthing is Executive Director of the Washington Area Bicyclist Association. Formerly the head of the Office of Green Economy in the DC Department of the Environment, Shane has been involved in the environmental planning and development of many projects currently changing the face of the District. Shane has graduate degrees in law and public policy from GWU and a Bachelor’s in Religious Studies from Virginia Commonwealth University.