Why we should account for air quality when planning bike lanes

A rendering of the proposed Cleveland Midway, a network of protected cycle tracks that would run across the city (courtesy of Bike Cleveland).

A rendering of the proposed Cleveland Midway, a network of protected cycle tracks that would run across the city (courtesy of Bike Cleveland).

In a lot of ways, cyclists get a raw deal. We ride a 25-pound machine on the same roads as people driving 2,000-pound steel boxes at high rates of speed. We struggle to carve out a small piece of the road, even as we get buzzed by passing cars or get screamed at by furious drivers who could kill us at a moment’s notice. There’s no such thing as a fair fight between a bike and a car. If I get into a head on collision with a careless driver, I lose.

Transportation people define cyclists (along with pedestrians, children, the elderly, and the disabled) as “vulnerable road users.” We are the ones most at risk of getting injured, or worse, in a collision.

For the most part, cycling and transportation safety activists have worked to try and bridge the yawning gap in safety between drivers and vulnerable users. So we push to implement road diets, to install bike lanes, to lower speed limits, to educate drivers and cyclists alike about road etiquette. And we do all of this, rightly so, in the name of safety.

The positives – and negatives – of cycling

Part of the impetus behind the push for improving bike infrastructure is the myriad benefits associated with active transportation, which I laid out in detail in my last post.

We all know the advantages of expanding cycling. It reduces wear and tear on roads. It improves safety for all road users. It helps promote vibrant neighborhoods and may increase retail sales. It can fight obesity and enhance public health. And it reduces local air pollution and helps tackle climate change.

But there’s two sides to every coin. We know that individual cyclists take a real risk each time they venture onto the road, even as the rise in cycling enhances safety for all. Could this same dilemma be true for air pollution and public health? The evidence seems to say yes.

Cyclists and exposure to air pollution

On the one hand, cyclists help to improve both local and regional air quality, full stop. Bikes are emissions free and every mile spent cycling rather than driving keeps roughly one pound of carbon dioxide (CO2) out of the atmosphere. The more people who move out of cars and onto bikes, the more we can mitigate transportation-related air pollution (TRAP) and reduce everyone’s exposure to its harmful effects.

it's a trap

Admiral Ackbar hates air pollution.

Yet, on the other hand, not every road user is exposed equally to TRAP. The specific characteristics of a vehicle can dramatically affect the levels of pollution that people riding in or on it can experience. We know, for example, that pollutants can concentrate inside of school buses, ensuring that children on board may be exposed to much higher levels of particulate matter and air toxics than they would otherwise. The same is true for heavy-duty truck drivers.

When it comes to drivers, however, that 2,000-pound steel box puts you at a significant advantage. Unlike cyclists, who have no air exchange buffer, drivers can roll up their windows and turn on recirculated air, lessening their personal exposure to TRAP, even as they produce it.

Multiple studies back this up. In a recent paper (paywall), Carlos Ramos, Humbert Wolterbeek, and Susana Almeida compared the exposure of cyclists and drivers to various air pollutants, using samples from Lisbon, Portugal. Though the authors found that drivers actually inhale five time as much carbon monoxide (CO) and more than twice as much CO2 as cyclists, respectively, the same was not true for other, more harmful pollutants. Cyclists were exposed to 30% higher concentrations particle pollution and ground-level ozone, on average.

As Ramos, Wolterbeek, and Almeida note, drivers tend to face higher concentrations of primary pollutants, like CO, because they remain in direct proximity to the pollutant source. Cyclists, in contrast, are able to limit their exposure to primary pollutants, but they breathe in much higher levels of secondary pollutants (ozone, PM2.5).

Exposure to pollution isn’t the whole story

It would be really consider convenient to end the discussion here and wash our hands of this whole issue. Drivers are exposed to higher levels of one type of pollution, while cyclists face higher levels of another.

But, like most things, this isn’t as simple as it can seem on the surface. The health effects of air pollution isn’t simply a product of pollution levels. Rather, it’s a function of concentration, length of exposure, extant health status (e.g. is the person elderly or asthmatic), respiratory rate, and inhalation route (nose or mouth).

When you account for these factors, the deck becomes decisively stacked against cyclists. Because cyclists spend more time on the road (due to their slower speeds) and breathe more heavily, they inhale higher levels of pollution in nearly every instance.

How cyclists can reduce their exposure to pollution

Now, there are steps that cyclists can take, at least in theory, to reduce their exposure to TRAP. Much like a cyclist can reduce his/her chances of being hit by using off-street paths or side streets, s/he can alter the amount of pollution inhaled by changing routes.

A group of scientists, headed up by Nathan Good from Colorado State University, explored this issue in a study published last fall. They selected a group of 8 commuters (4 bike, 4 car) in Fort Collins and equipped each of them with portable air monitors to document their levels of exposure along their daily commutes.

They found that, on average, cyclists were exposed to 18% more black carbon (a particular harmful component of TRAP) and 25% more PM2.5. Because cyclists spent more time commuting, the actually inhaled 92% more black carbon and 96% more PM2.5.

But Good et al. also found that cyclists could reduce these numbers by shifting to alternate, lower trafficked routes. Cyclists who used these roads less traveled actually took nearly one-quarter less black carbon.

critical mass

Cleveland Critical Mass in July 2015 as seen from my bike.

That said, there are some real issue with this study’s implications. Some people (including me) don’t have a viable, less trafficked route we can follow to work. Additionally, this approach shifts the responsibility for avoiding pollution intake from the public sector (policy makers, urban planners) to the individual cyclist. That’s a crappy way of doing things.

Including air pollution when planning bike lanes

Fortunately, additional research provides at least a partial answer.

In a 2014 study, Piers MacNaughton and colleagues looked at (paywall) how different types of bike routes affected TRAP intake among cyclists in Boston. They compared pollution levels along bike paths (those separated from vehicular traffic) and on-road bike lanes.

Unsurprisingly, the authors found that cyclists experienced significantly lower levels of air pollution while using off-road bike paths. But set that aside for now.

The important findings of this study are related to particular components of bike infrastructure. MacNaughton et al. found that two bike lane variables – vegetative cover and the number of intersections – significantly affect TRAP intake among cyclists.

Reducing the number of intersections a cyclist has to cross not only cuts his/her travel time, it also limits the number of idling vehicles s/he will face. And increasing the amount of vegetation between cars and cyclists can help slash pollution levels, as plants filter out a variety of air pollutants. According to the authors, a one unit increase in vegetative cover lowers black carbon and nitrogen dioxide levels by 3.4% and 11.6%, respectively.

As the authors conclude,

Cyclists can reduce their exposure to TRAP during their commute by using bike paths preferentially over bike lanes regardless of the potential increase of traffic along these routes. Based on these results and the relevant cyclist safety literature, urban planners should push for the development of bike paths instead of bike lanes whenever possible and should design bike paths with vegetation between the cyclists and the vehicle traffic.

Redefining the “vulnerable” in vulnerable road users

With all this in mind, the concept of “vulnerable road users” takes on a new meaning. Cyclists are not only at a greater risk of being injured or killed in a collision, we are also at a heightened risk of suffering the ill effects of TRAP.

Planners must start taking this into account. Bike infrastructure that may make sense from a safety standpoint may not hold up when we account for air pollution. And don’t get me started on vehicular cycling advocates. Cleveland’s decision to design bike lanes that buffer the curb already made no sense from a safety perspective. When you add air quality to the equation…?

Other projects seem to make more sense, in contrast. Both the Midway and the Eastside Greenway place vegetative buffers between cyclists and traffic. This feature provides a double dividend, as they would improve safety and help reduce pollution levels.

Ultimately, it’s time to broaden our horizons on bike infrastructure. Just as we shouldn’t expect indicidual cyclists to bear the risk of being run over to improve road safety, so too shouldn’t we expect cyclists to inhale poison so the rest of us can breathe cleaner air. Let’s start accounting for air pollution exposure and intake when planning bike lanes.

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