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posted by martyb on Thursday November 10 2016, @07:32AM   Printer-friendly
from the no-heavy-breathing dept.

Traffic-related air pollution in cities can be a significant health hazard in regions close to traffic areas. The hazard is particularly acute for those who primarily move through the area using their legs, namely runners, walkers, and cyclists, because the more energy they expend, the harder they breathe, and the more air they inhale. However, the harder they work, the faster they commute, so for a given distance traveled they are subject to less exposure time. The biomechanics of walking has been studied for many decades. Most of the research deals with energy expenditure and back in the 1950s it was observed that a person adopts a natural speed of walking that corresponds to a minimal expenditure of energy for a given distance. However, how hard someone breathes is not proportional to their energy expenditure, so the rate at which they naturally walk or cycle is not necessarily the rate they should move to minimize pollution intake.

Alexander Y. Bigazzi, from the University of British Columbia, wondered what the tradeoffs were and whether one could minimize their health risk by modifying their travel speed. He found that a minimum dose speed (MDS) could be determined that is from 2-6 km/h for walking and 12-20 km/h for cycling. This is a moderate level of activity of about 3-5 METs (Metabolic Equivalent of Tasks).

The study, published in the International Journal of Sustainable Transportation, builds on Bigazzi's earlier work, which found that exposure to airborne VOCs [volatile organic compounds] was 100 to 200-per-cent higher on high-traffic arterial routes and roads through industrial areas.

Blood levels of toxicants were 40 to 100-per-cent higher than normal in cyclists after riding just six to nine kilometres on heavily used urban streets. No difference in toxicant levels was detected in cyclists that used low-traffic streets.

[Continues...]

The abstract from the paper:

A higher active travel speed has offsetting impacts on air pollution inhalation dose through higher breathing rate but shorter exposure duration. The net effect of speed choice on inhalation dose for pedestrians and bicyclists has not been established. This paper derives equations for pedestrian and bicycle steady-state minimum dose speed (MDS). Parameter distributions from the literature are applied to a synthetic population of travelers to calculate individual MDS. Results strongly support the existence of a definable MDS, which is near observed travel speeds for urban pedestrians and bicyclists. For a wide range of travelers the MDS is 2–6 km/hr while walking and 12–20 km/hr while bicycling, decreasing with road grade at a rate similar to observed speeds. On level ground, pedestrian and bicycle MDS corresponds to a moderate intensity physical activity level (3–6 MET). Small deviations from the MDS have little effect, but large deviations (by more than 10 km/hr for bicycling) can more than double inhalation dose over a fixed distance. It appears that pedestrians and bicyclists choose travel speeds that approximately minimize pollution inhalation dose, although pollution is unlikely a primary motivation.


Original Submission

 
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  • (Score: 3, Insightful) by Dr Spin on Thursday November 10 2016, @10:28AM

    by Dr Spin (5239) on Thursday November 10 2016, @10:28AM (#425074)

    and the modest CO2 output from the bus engine can be shared between 50 passengers

    Its actually shared with the 50 people in cars and on bikes behind the bus. However, now our buses in London are hybrids, it is also a lot less than it was.

    The biggest cause of pollution is cyclists - who force drivers of large vehicles to drive in a lower gear by riding slowly in front of them. The difference for an HGV
    can be 1/4 gallon per mile. If a cyclist is causing four HGVs to drive two gears lower than they would normally (a common situation in London), then this
    amounts to the bike burning a gallon of diesel per mile. (OK, the problem is often two cyclists riding two abreast to prevent a bus or truck passing - so its
    only 1/2 gallon each).

    The problem would be worse if the cyclists did not keep killing themselves by riding into stationary vehicles.

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  • (Score: 4, Interesting) by Nuke on Thursday November 10 2016, @10:49AM

    by Nuke (3162) on Thursday November 10 2016, @10:49AM (#425081)

    The biggest cause of pollution is cyclists - who force drivers of large vehicles to drive in a lower gear

    Motor traffic is quite capable of holding itself up, and when I cycled in London a few years ago it was they who delayed me. Eg I did a regular trip from Mitcham to Acton (about 12 miles through suburbs in the rush-hour) which took me about 45 minutes by bike (overtaking some massive traffic jams en-route), an hour by train and about 90 minutes by car (which I rarely tried). I never killed myself BTW, although I did once see a car driver kill himself (and nearly another) by overtaking head-on into another car on the road along Wimbledon Common, just missing me (my narrowness saved me).

    Some of the trouble you mention is caused by people encouraged to cycle to be "green" but who really should not be cycling. I have always advocated a compulsory competence test for cyclists, including a demonstration that they can maintain a reasonable speed, 12 mph say, (which is more than the average vehicle speed on London).

  • (Score: 2) by Pino P on Thursday November 10 2016, @04:43PM

    by Pino P (4721) on Thursday November 10 2016, @04:43PM (#425177) Journal

    One workaround that I've seen in some parts of my home town is to reserve a lane on each side of the road for narrow, slow-moving vehicles.

    In my experience, the practical problem with city cycling is the dead red [pineight.com], or a demand-actuated traffic signal with an induction loop that fails to detect when a bicycle is stopped with its wheels on the crack in the road because of a bicycle's smaller metal surface area compared to a car or truck. I've seen dead reds that even a bicycle and a motorcycle combined cannot trigger. Some affected intersections have a "pelican crossing", a button that lets dismounted cyclists or other pedestrians request a crossing signal; others don't. Some jurisdictions allow cyclists to proceed with caution against a red traffic signal after waiting long enough to presume a malfunction; others don't.

  • (Score: 2) by JoeMerchant on Thursday November 10 2016, @04:44PM

    by JoeMerchant (3937) on Thursday November 10 2016, @04:44PM (#425178)

    Those hybrid buses also have significant negative environmental impact, it's just not in-your-face diesel soot.

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  • (Score: 2) by darkfeline on Thursday November 10 2016, @06:24PM

    by darkfeline (1030) on Thursday November 10 2016, @06:24PM (#425226) Homepage

    >The biggest cause of pollution is cyclists

    That's like saying the biggest cause of murder is vulnerable victims.

    The biggest cause of pollution (ignoring cows et al.) are the large vehicles.

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  • (Score: 2) by Dunbal on Thursday November 10 2016, @08:19PM

    by Dunbal (3515) on Thursday November 10 2016, @08:19PM (#425276)

    The biggest cause of pollution is cyclists - who force drivers of large vehicles to drive in a lower gear by riding slowly in front of them.

    The problem disappears if you simply drive OVER them... and you reduce global CO2 production to boot!