Which is safer: Bike without helmet, or drive without seatbelt?

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Cycling on Milwaukee Avenue at Grand Avenue and Halsted Street, one of the most crash-likely intersections on Milwaukee Avenue.

Someone asked me on Twitter: “What’s more dangerous, biking with no helmet or driving with no seatbelt?” It’s an odd comparison, but I decided to try to crack the question.

Here’s my answer:

If your definition of “dangerous” is “the likelihood that you’ll receive an injury while traveling in/on the vehicle”, assuming that the likelihood of being in a crash is the same*, then you are more likely to sustain an injury while cycling while wearing a helmet than while driving or being a passenger in a car while wearing a seatbelt.

Here’s the data, for crashes in Chicago in 2007-2010:

Table 1: Yes, recorded to be wearing a helmet while bicycling

Injury Type Frequency (each number is a person) Percent of total
No injury 3 7.32%
Possible injury 6 14.63
Non-incapacitating injury 26 63.41
Incapacitating injury 6 14.36
Fatality* 0 0
Total 41 100%

A value of 0 fatalities in four years for people wearing a helmet absolutely DOES NOT mean that a helmet prevented a fatality. The “contrary” data for “Recorded to not be wearing a helmet or having safety equipment” shows that there was 1 fatality in four years – the data do not suggest that the fatality would be prevented if the person was wearing a helmet. The sample size is so small that this data is meaningless.

Table 2: Yes, recorded to be wearing a seatbelt as driver or passenger

Injury Type Frequency (each number is a person) Percent of total
No injury 423,096 89.42%
Possible injury 21,667 4.58
Non-incapacitating injury 23,956 5.06
Incapacitating injury 4,338 0.92
Fatality 93 0.02
Total 473,150 100%

*I don’t think we can determine the likelihood of being in a crash when riding a bicycle because we don’t know the “device miles traveled” of Chicago cyclists. It’s probably possible to approximate the number of vehicle miles traveled by drivers in Chicago, though; I’m not sure about passengers.

Download the data for this article, which includes these additional tables:

  • Bicycling: All injuries
  • Bicycling: No safety equipment or helmet wearing
  • Bicycling: Unknown usage of safety equipment
  • Auto: All injuries
  • Auto: No safety equipment or helmet wearing
  • Auto: Unknown usage of safety equipment

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About Steven Vance

Enthusiast for urbanism, bicycling as transportation, and open data. Building a bicycle culture in Chicago.
  • WITTCO Gmbh

    I see the helmet-seat beat comparison used quite often. I thi k it is used because it seems logical. However, it is not. The devices are used for different purposes (agreed, the ultimate goal, safety, is the same). A belt is for stopping the driver from going forward. A helmet is for reducing impact injury (supposedly…because there is a body of data out there that say this is not true).

    Most people wear seat belts. I always do. Require it in my car because it is a heavy, fast moving vehicle that when I drive, I am interacting at speeds and with others that increases likelihood of collision.

    Thanks for sharing your found data.

    • http://www.stevevance.net/planning Steven Vance

      I wanted to qualify the helmet’s use: It’s for reducing injury to the head, and maybe not even the head, but the brain (I still don’t understand what it’s supposed to do, or if it’s good at that).

      Since I made this at 4 AM, I couldn’t expand on “why this is a weird comparison”. I don’t think it’s a comparison that people should be making. And I also lack exposure data (how many miles people bike versus how many miles people bike). Even if I had that, it would still be hard to say which is “safer” (again, what is the definition?). 

      Is my definition of “safer” okay? The lowest likelihood of sustaining an injury?

  • Mark Elliot

    I suppose one can use mode split (proportion of commuting trips made by bike, say) as a proxy for general bike use if we want to put these data in proportion. But of course it’s horribly imprecise. 
    Maybe mobile phone geo-locating presents an opportunity to sample traveling patterns among some representative set of cyclists to better assess the true prevalence of cycling, rathe than roughly impute it from self-reported surveys.      
     One tantalizing possibility looking ahead for understanding trends in motoring is the ‘vehicle miles traveled’ metric that’s sometimes proposed for road/transportation funding (in lieu of the gas tax). Right now we have  accurate gross tallies of total miles driven, but not much on the household level except for self-reported travel survey data. Were that data to be tracked, though, we’d have a finer-grained picture of motoring habits, and in the aggregate, by inference, a more accurate view of mode choice over time than we have now. Especially if the policymakers succeed in metering miles driven, we’d see a real shift, IMO.   

    • http://www.stevevance.net/planning Steven Vance

      Jennifer Dill of Portland State University gave GPS devices to cyclists in Portland and used that data to assess how people chose their routes, and which bikeway facility types they encountered in those routes. She found that many people would extend their route (from the least distant route) in order to use bikeways. 
      http://www.ibpi.usp.pdx.edu/bikegps.phpThere are many smartphone apps that can track users, and one from San Francisco, California, CycleTracks, was designed expressly for the purpose you describe. 

      I did come across some new data I haven’t worked with before, that of the Chicago Metropolitan Agency for Planning’s “Travel Tracker”. It’s essentially a household travel survey much like the National one. But like that survey, the sample size is pretty small, although likely larger than the National one’s sample of Chicago-area households. 

      Other data I know about but haven’t incorporated into my research as much as I should is rail station access. Both the CTA and Metra measure the access mode of their passengers, but very rarely. The data is available on RTAMS. 

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  • http://tumblr.tryingtofollow.com ariahfine

    Hey, this is really interesting data. Can you tell me where you got it? I’m curious if there’s stats on the actual number of riders/drivers and the injuries as a percentage of those. 
    The question I’m really curious about: Is riding a bike without a helmet safer than driving a car with a seatbelt?