Why You Have to Wear a Seat Belt, but Can Drive a Motorcycle

Why, in many states, is it against the law to drive a car without wearing a seat belt, while at the same time completely legal to own and drive a motorcycle – sometimes even without a helmet? If riding a motorcycle is 20 times more dangerous than driving a car, and 4 times more motorcycle accidents result in injury or death compared to car accidents, should this really be the case?

This got me thinking. Do states with strict seat belt laws also have strict policies on motorcycles? Do they also tend to be stricter on speed limits and other policies enacted in the name of public health? Should states’ laws be consistent with each other? How do these laws vary with political party? Are Democratic states more likely to have strict laws than Republican states?

To answer these questions, I dug up some data from the U.S. Department of Transportation, the Insurance Institute for Highway Safety, Gallup, and The Tax Foundation. Specifically, I found information on seat belt laws, motorcycle helmet laws, freeway speed limits, seat belt adherence, the tax rate of cigarettes, the percentage of a states’ population that leans Republican, and the traffic death rate per 100 million miles of road traveled. I combined the traffic law data to create a metric for comparing the strictness of states’ motorist legislation and began looking at relationships.

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First, I wanted to explore whether states are consistent in enacting legislation that tries to get people to abide by policies that are good for their health.  In some ways, states’ laws are consistent, but in more surprising ways they aren’t. On the consistent side, states that had low freeway speed limits, were more likely to have strict seat belt laws (p=0.047). Similarly, states with lower speed limits were more likely to have high cigarette taxes as well (p=0.001). Oddly enough, however, states that passed strict seat belt laws were no more likely to pass strict motorcycle helmet laws (p=0.60) and states with high cigarette taxes were no more likely to have high alcohol taxes (p=.50). It seems that states are fairly inconsistent in passing legislation for the sake of public health. You would think that if you are going to enact legislation to force people to wear seat belts, you would also force motorcycle riders to wear helmets. Similarly, if you are going to tax cigarette consumption, shouldn’t you tax alcohol consumption as well? This is like mandating that everyone must wear sunscreen at the beach, but not if you go to a tanning salon. Regardless of what you think the right answers are with regards to taxation and the government’s role in our own personal decisions, can’t we agree that the law should at least strive to be consistent with itself when possible?


Despite inconsistencies in state legislation, there are patterns in how states chose to enact policy. When consistency in state laws exists, what dictates whether states are strict or lenient in protecting people from themselves? Intuitively, it seems Republican states would interfere less in people’s lives than would Democratic states. The data indicates that this is exactly the case. States with a high percentage of Democrat residents are much more likely to have high cigarette taxes as well as strict traffic policies (p<.001, p<.001). Along the same lines, Republican states are more likely to have high speed limits and lenient penalties for not wearing seat belts.


So how do these differing policies translate into road safety in states of different political leanings? For one, seat belt usage is much lower in Republican states than Democratic states (p=0.003), and for every additional 10% of the population that leans Republican, the percent of people that wear seat belts goes down by about 10 percentage points. As a result, Republican states tend to have higher rates of traffic deaths (p=0.001). In fact, increasing the percentage of the population that leans Republican from 40% to 50% is correlated with a ~40% increase in the rate of traffic fatalities. Republican states tend to be more lax on their road rules, which is great if you really don’t want to wear your seat belt or you want high speed limits, but it likely does come at the cost of some lives every year.


So if you are a state considering various policies to lower the traffic death rate, how do you get the best bang for your buck? The data shows that the single largest effect on traffic deaths is the speed limit on freeways (p=.002). States with speed limits of 75 mph have roughly 50% higher traffic mortality than states with speed limits of 65 mph. If you don’t want to change the speed limit, the next best option is to increase seat belt usage (p=.007). Increasing seat belt adherence from 80% to 90% is correlated with a reduction in the rate of traffic deaths of nearly 40%. In fact, the data shows that achieving such an increase in adherence could be accomplished by moving from the most lenient seat belt policies to the strictest.

The speed limit policy infringes on personal liberty less, has higher efficacy, and benefits every person involved in an accident – not just the non-seat belt wearers.  Strict seat belt policies, on the other hand, only affect the seat belt wearer and definitely call into question the limits of legislation on personal freedom. If the repercussions of not wearing seat belts only affect the decision maker, its hard to argue that society as a whole bears a significant cost as a result of people not wearing seat belts. 

I would argue that lowering speed limits is the best potential option legislatively if your goal is to minimize traffic deaths while preserving personal freedom, but should be weighed against the economic costs of such a decision. Seat belt laws, while lowering traffic deaths, are less effective, infringe on personal liberties, are much less likely to be consistent with other laws, and lead to a slippery slope of when it is okay for the government to intervene in personal decision making that does not have a significant cost on others. This is not to say that we shouldn’t try to increase adherence to seat belt wearing through other means, but fines are likely not the best way in this case.


So where does this leave us? Seat belts work, you should wear them, but the government probably shouldn’t tell you to. Driving faster leads to more traffic deaths. The law is inconsistent with itself, but shouldn’t be. Driverless cars would be awesome and would make all of this moot. Take all statistics with a grain of salt.

And as for why we have to wear our seat belts, but are allowed to ride motorcycles without helmets? Blame the biker lobby.

For some additional articles on this topic:

Red states have more traffic fatalities than blue ones, but why?

A Comprehensive Overview of Seat Belt Research

12 thoughts on “Why You Have to Wear a Seat Belt, but Can Drive a Motorcycle

  1. Pingback: 3p – Drive in a Red State? You’re More Likely to Die. Here’s Why | Profit Goals

  2. Pingback: 1p – Analysis Finds States’ Laws Are Inconsistent with Each Other | Exploding Ads

  3. Interesting work. One comment: the cost of lower speed limits is different in smaller, high-population density states (which tend to lean Democratic) than it is in larger, lower-population density states (which tend to lean Republican). The extra percentage of your life spent sitting in a car if the speed limit is 55 instead of 80 is probably negligible if you live in Delaware, but not at all negligible if you live in North Dakota. So the difference in the speed limit in red states may not only be due to political philosophy, but also due to the practical tradeoffs. You’ll never get to 80 mph anyway if you live in NYC, but if you live in western Texas and your job is 30 miles from where you live, you will look at things differently no matter what your opinions on taxes, abortion, or Obamacare.


  4. Umm… here are a few points you might consider:

    You didn’t mention attempting to account for age effects. This is a fairly significant factor.

    You didn’t mention trying to separate out impaired drivers. Driving impaired is frankly stupid and not just dangerous for the stupid person.

    It’s interesting you found a correlation between maximum speed limit and fatality rate. That probably is either not a causal correlation or is some kind of artifact in your analysis. These two reports indicate that most fatalities occur on non-interstate roads. Speeding is involved, but given that they are minor roads, the speed involved in the crash is probably lower.

    Here’s a link to a DOT paper that covers what were considered the major factors (from 2008)

    I don’t know where you would get the data, but I think it would be more interesting to see if different driver training requirements had an impact on fatalities. The other problem is that they tend to change over time.


  5. Well done. I would be curious… any stats on these [completely illegal] photo radar cameras for speeding? i feel like it’s more of a Blue state thing…. but then again.. i’ve been wrong before, thoughts?


  6. Be careful: Cum hoc ergo propter hoc (“Correlation does not imply causation”)! Sometimes in the article I felt like I was on this blog: http://www.tylervigen.com/spurious-correlations

    Additionally: “Blame the biker lobby”…really? You should blame the government for acting irrationally (or at least not in a consistent manner). Sometimes they are listening to the public, sometimes only to some seemingly important people but most of the time they do what the economy wants…

    Liked by 1 person

    • Totally agree with you, definitely think these should be taken with a grain of salt and I mention that at the end.


  7. I ride a motorcycle daily, also live in Oregon. We didn’t always have a helmet law they made it a law when some guy crashed when I was about 7 the mother pushed the law because a helmet would of saved her son. Our speeds are low, 55 in most and 65 after troutdale or tigard. The most dangerous things for a bike rider is 1 excessive speed, 2 cars cutting into the other lane riding or driving to close, and most of all common sense. We road from Oregon to Arizona even though Arizona has optional helmet I refuse to ride without one, or without my gear and pads.


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