More on why what mode, route chosen for commuting matters

Every now and then, the air-quality value of bicycle versus car commuting is called into question. Such is the case in today’s thread. In fact, the California Environmental Protection Agency Air Resources Board (ARB) in its “Study: Commuters’ exposures to air pollution greatly depends on mode of travel: Sacramento area study shows light rail commuters experience lowest pollution levelsnews release observed: “Since the average car and public transport trips are much faster than bicycle trips, they may offer shorter exposure durations; however, cycling has significant health benefits.” The study being referred to – also for your edification – is titled: “Commuter exposure to PM2.5, BC, and UFP in six common transport microenvironments in Sacramento, California.” It was “conducted by researchers at the California Air Resources Board (CARB),” and “was published recently in Atmospheric Environment, a prestigious scientific journal in the field of air pollution,” the ARB offered. (There is more about this study both here and here).

To this the authors of the “The Fort Collins Commuter Study: Impact of route type and transport mode on personal exposure to multiple air pollutants” article (published in the Jun. 2016 Journal of Exposure Science & Environmental Epidemiology issue), add: “Given the ubiquitous and insidious nature of air pollution exposure, strategies are needed to help individuals reduce their daily intake. Such strategies can be impactful, because there is no ‘safe’ level of air pollution exposure and because the largest marginal benefits to human health are hypothesized to occur when relatively low exposure levels are reduced further (given the log-linear nature of exposure-response for many health outcomes). Replacing short car journeys with cycling has the potential to produce health benefits for both the individual (through increased exercise) and the general public (through reduced emissions).”1

Expanding upon this further, let’s consider commuting by bicycle along a heavily vehicle-trafficked thoroughfare whereby encountered en route are plenty of signalized intersections. Let’s also consider cycling along a designated trail that is situated in close proximity to a paralleling highway where during the time of travel, highway traffic is moving unimpeded or on a street where motor vehicle traffic is, for the most part, lacking.

In stop-and-go traffic, vehicles are periodically paused. During this time in which said vehicle engines are idling and therefore are not burning fuel as efficiently as those continuously on the move, exposure by bicycling commuters to corresponding pollutants may be much greater than what an average bicycling commuter might be exposed to while riding in close proximity to a paralleling highway or on a street mostly devoid of motor vehicle traffic. With this in mind, route choice may play into a bicycling commuter’s choosing which route to take.

On the other hand, there are those who may choose to forego the bicycle commute altogether because, given the choice between say cycling along a heavily trafficked thoroughfare with stop-and-go traffic (intersections encountered) and driving a motor vehicle along said road, the latter may just have a higher air quality value over the distance covered. In a motor vehicle, the car’s interior atmospheric conditions can, to a large degree, be controlled such as in having windows rolled up and the control which sets inside atmospheric condition, then placed in the recirculate position and under such condition or control, thus limiting the amount of outside air entering the car’s cabin.

I was faced in 1978 and ’79 with just such a situation when I worked six miles from where I lived in Mountain View, California. I remember the times I used to travel to work very vividly. It was as if it were yesterday.

Commuting by car – and back in those days, motor vehicles weren’t nearly as clean-burning and fuel efficient as they are today – took approximately 30 minutes to cover the six miles in the morning peak-hour commute (which I was part of) and roughly 45 minutes to cover the same half-dozen miles during the period of peak-demand in the late afternoon.

Had I traveled by bicycle, it may have taken less time, the same amount of time or more time, depending, and I can only think of one route I could have used where I would not have been exposed to the level of pollutants emanating from vehicles like on the route I did use when I commuted by car. However, I believe in doing so, time to get to and from work would, at best, been the same and at worst, and most probably, longer.

Interestingly, there were two other options. These were also covered in the Air Quality Matters “Study analyzes pollution’s effect on daily commute” post of Sept. 6, 2017 these being bus and train.

It is presumed that where I lived in Mountain View, I would have had access to a bus that could have picked me up near to my apartment and dropped me off near to where I was employed. If not that, then maybe through a transfer the same would result. However, the time required for the bus to provide this service might have been considerably longer than what it took me to get to and from work by car since, presumably, buses would encounter the same level of congestion no matter the route taken.

As to using the commuter train, a fourth alternative, there was a station located adjacent to the apartment I was living in, so access to such wasn’t a problem. This service, more than likely, would have been the speediest, even with the additional stops en route, but, based on where the station located nearest to my place of employ was, how to get from the station to my final destination was, figuratively, where the monkey wrench was thrown into the situation. I don’t believe there were provisions on the then Southern Pacific’s passenger cars or at the stations for bicycles. So, that would mean hailing a taxi at the Sunnyvale station; it was either that or having access to a transit bus that could provide shuttle service between the station and work and back each day. That said, the same limitations might not be a factor today, though, and I would hazard a guess that the car commute using the same exact route would be even longer during said peak commuting times.

And, of course, weather is always a consideration while distance factors in also.

There is much more on air quality as it relates to commuting here and here.


  1. Nicholas Good, et al. “The Fort Collins Commuter Study: Impact of route type and transport mode on personal exposure to multiple air pollutants,” Journal of Exposure Science & Environmental Epidemiology 26(4): 397-404 (2016, Jun.)

– Alan Kandel