An Argument for Separated Facilities, Slow Cycling, and Fewer Cars

A study conducted by researchers at the transport research institute at Hasselt University in Belgium, found that bicyclists inhale five times as many toxic nanoparticles as drivers and pedestrians on the same streets. Proximity to tailpipe pollution as well as higher respiratory rates account for the higher particle intake. This is the first time both respiration and particle quantity were simultaneously measured in a study of this kind.

This is obviously bad news for bike commuters who currently ride in heavy traffic. The knee-jerk reaction would be to say that bicyclists should ride less. Of course, we know that many of the most deadly diseases are closely linked to a sedentary lifestyle, so riding less has its own dangerous side effects. Better solutions include more separated facilities to enable bicyclists to put together commutes that bypass major arterials and heavy automobile traffic, riding slower to keep your respiratory rate down, and of course, fewer cars on the road.

More at Grist

29 Responses to “An Argument for Separated Facilities, Slow Cycling, and Fewer Cars”

  • Franck says:


    First, congrats for your blog. I read it every day here in Paris, France, and I’m a big fan !
    I’m very surprised to read this post, as I was, since feb 2009 happy to know that I was less exposed than cars or even bus users to particules and N02 as a Bicyclist in Paris. i’m sorry I have no time to translate the whole document, but this study has been achieved by a very serious institution in Paris, and results were pretty clear….
    You could probably still have a look to interesting graphs in this document, unless you read french… :
    I will carefully read these results from Hasselt University, thanks for this information.

    All the Best,

  • Yangmusa says:

    This seems to be somewhat contradictory to a 2005 study by the British Heart Foundation. While it found that cycling in heavy traffic definitely means cyclists breathe in a lot of pollution, the level of pollution inside cars is actually 3 times higher than outside because car ventilation systems suck air in at ground level.

  • Alan says:

    @Franck, Yangmusa

    If I’m understanding this correctly, the difference is that this new study took into account the respiratory rate of cyclists versus peds and drivers, whereas the other studies didn’t.

  • Adrienne says:

    Sucking exhaust is the main reason why I do not wait behind cars at intersections. I usually wiggle to the front to get away from it.

  • RDW says:

    Wow, depressing. But I have to believe that the lowered stress level a bike commuter has vs a driver stuck in traffic still leaves the cyclist with a net gain health wise.

  • Wannes says:

    Hi Alan,

    I’m from Belgium and I would like to add some info. This study was done in Belgium and you should know that the Belgian government has promoted diesel cars as long as I can remember…
    Diesel cars produce less CO², but far higher levels of toxic nanoparticles.
    Belgium is, as you all know, very small and a real transit-country. A great deal of the European transport, diesel trucks off course, passes in Belgium. Belgian companies can deduct the costs of company cars for their employees, and off course they all recieve a diesel engined car…

    All this leads off course to enormous amounts of toxic nanoparticles in the air, especially in the cities. This can explain the high rates found by the researchers.

    On a second note, one can ask himself what the health benefits of cycling to work are…

    Greetings from Belgium!


  • Lovely Bicycle! says:

    Hmm. But what about those studies supposedly showing that being inside a car meant exposure to *more* exhaust than cycling in heavy traffic? I have seen lots of references to these studies, though have not read the original research.

  • Lovely Bicycle! says:

    Ah, never mind – I’ve read the comments above.

  • Alan says:

    @Lovely Bicycle!

    IIRC, those older studies didn’t take into account the higher respiratory rate of bicyclists compared to peds and drivers. The U.K. Times reported that this is the first study to look at both particulate matter and respiratory rate to get a total. Hence, my comment about slow riding.


  • Alan says:


    We’re leap-frogging comments! No problem… :-))


  • dave says:

    My commute runs next to several busy highways and also past the local dump. Last year I noticed that I was getting a lot of respiratory infections. I researched and found a sport mask that was made specifically for filtering pollutants, bateria and pollens. I wear it every time I ride my commute now and my lungs are very grateful. It does make it a bit harder to inhale, but for me it’s not any worse than being at altitude. I’m also pretty happy to have it on when I ride through a swarm of no-see-ums.

    The most effective way to introduce toxins into the body is through inhalation. Breathing in pollution should not be taken lightly. Not only are you breathing harder when you ride, your circulatory system is transporting whatever you breathe into your system faster too. To argue that sitting in a car is more toxic than riding a bike doesn’t negate the problem.

  • Ed L. says:

    The “slow riding” to reduce respiratory rate so as to reduce exposure to particulates sounds intuitively correct, but wouldn’t a slower ride also mean a higher exposure time? Go fast, inhale more per minute over a shorter time span; go slow, inhale less per minute over a longer time span. My intuition is that the increased exposure time may even out any benefit gained from the lowered respiratory rate.

    There may very well be a benefit for less energetic riding in high pollution situations – I am specifically thinking of what might be the effect of “deep inhalation” versus regular inhalation of particulates – but, I not sure that the “slow is better” logic is quite so sound as it seems from first blush.

    (Also, I am going to go with my own personal bias on the overall health effect likely being positive for commuting cycling in all but the most severe pollution situations, since the incidentals from the lowered stress and aerobic activity likely compensate for whatever increased particulate exposure one might get. But I would like to see further research on the issue, to be sure.)

  • Alan says:

    @Ed L.

    That’s an excellent point, Ed. I guess my experience has been that up to a certain speed (approx. 12mph) my breathing stays relatively even, then when I push just a bit harder, my breathing jumps up dramatically; in other words, it doesn’t seem to be linear. I agree, it would be great to see further research on this issue.


  • demimismo says:

    This is like saying drinking is the problem in an area where the water is polluted, the problem is not with the cycling but with the polluters.

    If cyclists and pedestrians are exposed to insane amounts of whatever thing produced by cars, then we should focus on discouraging car use, not in getting bikes out of the road.

  • Alan says:


    While I totally agree in principle, at least here in the U.S., the idea that we’re going to suddenly clear the road of cars is not realistic in the least. In the meantime, the people out there on bikes sharing the road with cars should be aware of the potential health risks and take whatever precautions are reasonable to minimize their exposure.


  • Tal Danzig says:

    I try and make a point of keeping a couple metres between me and any cars in front of me when stopped behind a car at an intersection. I figure there’s no need to suck air directly from the tail pipe! Not sure how much difference this makes, but the air a bit back is noticeably cooler than the air right behind a car. While the tendency when stopped is to creep right behind or to the side of the car in front, I usually prefer not to be re-passed by the same cars just to save a few second, and of course keeping distance while moving is just common sense! I’ll admit when I know I’m moving faster than the flow of traffic, or when I can leapfrog cars making right or left turns, I will try and get around to the front.

  • demimismo says:

    Alan, you are right: cyclists should be aware of the dangers involved in urban cycling. As Tal said, they could just leave a couple of meters when waiting behind a car.

    But saying that this study is an argument for segregation is a complete misinterpretation.

  • Alan says:


    “But saying that this study is an argument for segregation is a complete misinterpretation.”

    We’ll have to agree to disagree on that point.


    PS – And, of course, I agree that we need to do everything we can to discourage automobile use.

  • demimismo says:

    We can disagree, ofcourse :-)

    But if you are gonna take that study seriously, think twice. They are counting the amount of nanoparticles inhaled by cyclists, but I have not read anything about exalhation (we are not closed recipients). With higher breath rate comes stronger exhalation.

    Also, when you are inside a car you are inhaling polluted air that doesn’t get easily renewed. When you are outside, maybe cycling, you are breathing constantly renewed air.

    Mmmm… maybe the article that generated all this controversy is written by people that are also saying that world may not be warming? ;-)

  • Runjikol says:

    Thankfully in my part of Melbourne, Australia, I have well-separated cycling tracks to use on my commutes. The city as a whole is quite green with trees almost everywhere except the newest developments. An earlier poster mentioned anti-pollution masks which I have considered on the occasions I go into the CBD (uptown?). They are pretty cheap and I’ve seen some models that are less than $50. The filters are replaceable, too. A small investment to look after your health. Sure they’ll make breathing a little harder but that will increase your respiratory fitness! So it’s a win-win: major reduction of inhaled toxins, minor increase in aerobic fitness, and for less than $50!

  • demimismo says:

    Runjikol, anti-pollution masks don’t stop toxic nano-particles. The same happens with air filters installed in cars :-(

  • Runjikol says:

    The one’s I’m referring to filter to the PM10 level or the HEPA level. More than adequate filtering at the sub micron level. I’m not talking about those pressed paper filter masks for bird flu and the like.

  • Bikes aren’t hard to see if drivers pay attention « BikingInLA says:

    […] behavior or focus on the big machines that can kill people? Slow riding on separated bikeways means sucking in less smog. Michigan may follow California’s lead and ban texting while biking. Pondering empathy for […]

  • Jack Bulkley says:

    Luckily I spend most of my commute on paved greenway trails aways from the cars. Even the other parts of my commute are on quite residential streets. I usually have a couple of mornings in a row with 0 passing me in the same lane. An average is probably 2 or 3. I am not sure how many times there might be one close enough to cause me to breathe significantly more fumes.

    I would also point out something I noticed when visiting Las Vegas earlier this year. There are nice bike lanes on the quite Alta Drive which parallels Charleston Blvd which has the heavy car traffic. To me this gives bikes a much nicer ride even though the lanes are not completely separate from the cars.

  • Frank says:

    Don’t worry about it. They eventually found that caffeine, eggs, now beef are all good for you. Some university will do a study and find that exhaust has anti-oxidants in it, the media will pick up the story, and we’ll have more heavy breathing cyclists crowding the streets than we know what to do with. Then another university will study it and it will make it on CNN and ridership will go back down after the study reveals that there is more rubber residue left behind by all these bikes that an equal number of Mini-Coopers.

  • peteathome says:

    While I would certainly enjoy doing my transportational cycling on quiet, separated routes that easily connect me from point A to B, I think that is infeasible in most urban areas where the pollution is highest. There simply are not available routes where you could build separated paths. The best you could do is build sidewalk-like sidepaths next to the road, which really don’t get you out of the pollution stream and which introduce serious traffic risks that I would fear much more than the long-term pollution effects.

    I do try to avoid arterials if my route allows it, especially in the summer when the combination of the heat from all the cars and pollution is really unpleasant. Although I have to say that the air on busy streets is a LOT pleasanter now than it was in my boyhood in the 60s and 70s. You have no idea what it was like riding behind 1960s era cars and buses

    Maybe in suburban areas alternative routes parallel to the arterials could be developed within the existing street grid. To allow the side streets to be used to get around some side streets would need traffic lights put in to allow crossing the arterials, but with measures to keep these streets from becoming routes used by drivers to bypass the traffic. Berkely, CA had been experimenting with such ideas.

  • peteathome says:

    Nanoparticles – Early studies were primarily looking at levels of pollutant gases such as carbon monoxide in bicyclists blood compared to drivers. Bicyclists actually came out better. You may breath more in, but your bady eliminates the gases faster when you are active.

    But some studies warned that very tiny particles, combustion particulates, I think, associated with diesel burning were different. A lot of this shows up a soot when diesel vehicles accelerate. These tiny particles tend to get trapped in lung tissue. So whatever you breath in might stay and this stuff has been associated with lung problems.

    Bicyclist inhale more of them due to their higher breathing rate than sedentary passengers and what is breathed in might not be eliminated.

    The good news – this was a Belgian study. There are a lot of diesel passenger cars there. In the USA we have almost no diesel passenger cars, just diesel trucks and buses. In my area most of the diesel buses have a low emission technology, so it may just be trucks here.

    The bad news: many people are promoting diesel passenger vehicles for the USA as they get much higher mileage than gasoline vehicles of the same class, and a gallon of diesel takes less oil to produce than a gallon of gasoline.

    I wonder in the newer diesel technologies that are suppose to be cleaner, such as Volkswagon’s TDI engine, reduces these particles?

  • Garth Madison says:

    @demimismo: Unfortunately, exhaling does not necessarily eliminate inhaled toxins. The problem is in exposure of the lungs to the toxin, and absorption into lung tissue or the blood stream. Higher respiration rates increase the amount of airflow and how deeply and effectively you are getting the air down into the alveoli to exchange gasses with the blood. Exhalation occurs more rapidly, but only after the exposure, and thus after the potential transfer of toxins. Think of friable asbestos fibers as an example. Once those fibers are in your lungs, they embed themselves in the lung tissue. The faster your breathe them in, the more fibers become embedded, and breathing out faster does not help you.

    I see two potential solutions: 1) limiting the cyclist’s exposure, and 2) reducing the sources of pollution.

    Limiting exposure can include segregation. I certainly try to avoid traffic as much as possible, both to minimize my risk of being struck by traffic (my city has woefully poor bicycling infrastructure), and to limit exposure to pollution. Avoiding traffic also tends to make my commute a more pleasant one, and the bike affords me more opportunities to do so than the car does. Luckily, I am blessed with a mostly residential bike route between my house and my office. I will sometimes try to hold my breath when I approach a car or lawn mower (or smoker, for that matter), especially a particularly noxious one, for whatever good it does. But mostly my hope is to stay in fresher air and enjoy the outdoors. I would note that cars are not the only source of pollution – many urban areas have industrial or energy plant related pollution as well. And lawn mower engines are more noxious than cars, because they are obsolete two-stroke engines with virtually no regulation of emissions.

    Of course, reducing pollution sources is a lovely idea, and a necessary goal, but unfortunately the longer term and entirely uncertain solution. Some progress has been made towards introducing emission regulations on lawn mower engines in recent years. The feds have strict emissions regulations on diesel engines in the U.S., and diesel automobiles are cleaner now than ever. Really, I have no problem with modern diesels, and in terms of environmental sustainability would prefer to see diesels than solutions like the ill conceived E-85 vehicles (who looks for efficiency by switching from a fuel with a higher energy potential to one with less?). The larger perspective is a consideration of habit and cultural priorities. The U.S. has so mired itself in an automobile-centric culture that driving has become ingrained habit, and automotive infrastructure has enveloped the landscape. Reducing pollution would require nothing less than fundamentally altering our built environment and changing the decades long habit of millions of commuters. But in a world where every other ad on TV is for cars or auto insurance, and the supposedly green and financially sound policy course is to pay people to remove used cars from the road and buy brand new ones for minimal gains in fuel efficiency in order to prop up an automotive industry that was deemed too big a component of our economy to allow to fail, the chances of forging global or even national changes in a realistic time frame are questionable. Capitalism is an inconstant friend.

    I suppose a hybrid solution would be to advocate for bike infrastructure that segregates cyclists from auto traffic. I certainly wish my city would add such bike routes. Unfortunately, depending on where you live, that kind of solution may seem more or less certain, or even akin to the pipe dream of reducing the number of cars on the road.

    I think that leaves us where Alan suggested – continuing to educate ourselves about the risks of our daily activities, and taking what precautions we can. While doing so, we can continue to work on the larger problems, and maybe even see occasional progress. For instance, the vehicles that offend me the most are those that clearly have massive mechanical failings, and are spewing vast quantities of oil and god knows what else out of their tailpipes. Some states require emissions tests as part of licensing, others do not. If your state doesn’t, maybe you could work towards getting them to start. If they do, find out how enforcement works and report violators. Sometimes I think 10% of the vehicles out there are responsible for over 50% of the pollution. Removing them would be a good start.

    In any case, biking less is not the answer. I believe that biking provides a net health gain, despite any increased exposure to toxins. In other words, the driver getting gassed by pollution in his steel shell will, on average, have more health problems than the biker getting gassed on the road, because the biker is healthier to start with because of the regular exercise he is getting, the lower stress levels he may experience, etc. As demimismo said, polluters are the problem, not cyclists, and I would submit that silently acquiescing only exacerbates the problem.


    (Btw, Alan, I recently discovered this blog, and would mention that I am greatly enjoying it. As others have stated, your photography is beautiful and inspiring, and adds immeasurably to the site.)

  • Adrian says:

    “The knee-jerk reaction would be to say that bicyclists should ride less.”

    Really? My knee-jerk reaction would be to say that people should stop driving. Knowingly poisoning innocent strangers should be heavily restricted, if not banned outright.

© 2011 EcoVelo™