Category Archives: Environment

Car Emissions vs. Car Crashes: Which One’s Deadlier? The answer actually surprised us.

Eric Jaffe at CityLab discusses my post from Monday:

The ever-thought-provoking David Levinson posed a question at his Transportationist blog earlier this week that’s worth a longer look: Are you more likely to die from being in a car crash or from breathing in car emissions? If your gut reaction is like mine, then you’ve already answered in favor of crashes. But when you really crunch the numbers, the question not only becomes tougher to answer, it raises important new questions of its own. …

Death by car: Are you more likely to die from a crash or breathing its toxic emissions?

Should you fear more getting hit by a car, or breathing in its toxic emissions?
I recently engaged in a conversation with my colleague Julian Marshall about which kills more : Deaths by vehicles (cars plus trucks) from crashes or deaths by vehicles from air pollution. I of course defended the “honor” of transportation and said death by crashes was much larger, he is an environmental engineer looking at air quality, and thought that was very important too. (He also argues death from car emissions is just as “honorable” as actually getting hit by a car.)
It turns out, Deaths by Crashes is larger, according to official sources, but not as much as I expected. And, the answer depends on what metric you use.
In the US, according to the Global Burden of Disease Study (Data Link), for 2010, for men+women:
road injury + other transport injury total air pollution
Deaths: 15 36
DALY: 797 624
Years of life lost: 653 565
Notes: Units: deaths per year per 100,000 people; DALYs [Disability Adjusted Life Year] per year per 100,000 people. Air Pollution is Ambient Particulate Matter air pollution and Ozone, not just transport related pollution deaths. Road injury plus other transport injury is comprehensive, the vast majority are road injuries, the large majority of which are due to car. This  includes things like driving off a cliff as well as driving into pedestrians.
Those numbers include only fine particles (PM2.5) and ozone. Using the numbers above, air pollution is worse than crashes in terms of total deaths, but not in terms of DALYs and Years of life lost.
We also need to figure out the fraction of total air pollutio n that is due to road transport.
Julian says:
Just as estimating deaths from air pollution is inexact (no death certificate says “air pollution” as cause of death; instead rates of outcomes like heart attacks are elevated slightly in the presence of air pollution), so too it is inexact to estimate contributions from specific sectors (e.g., road transport) to the air pollution total. Some PM2.5 is emitted directly and some pollution forms in the atmosphere from chemical reactions of precursor emissions; the latter type (called “secondary PM2.5″)  is harder to attribute.
An MIT study estimates that proportion at 25%. Notably they also come up with more annual deaths from air pollution at about 200,000 per year in the US (rather than the 100,000 or so the GBS study implies). Air pollution deaths (premature strokes, heart attacks, lung problems, and so on) on average shortens life by 10 years per person who dies from air pollution. Car crashes are more likely to shorten life of younger persons, hence the greater years of life lost per death.
Julian says:
The most useful number to look to, from an overall health standpoint, probably is the DALYs, since that number includes both mortality and morbidity (death and disease).
Accounting for uncertainty, to a first approximation the numbers above are roughly comparable to each other, for the two causes.
 I would conclude we should fear crashes more than air pollution from traffic, but we should not be sanguine* about emissions either.

*Our temperments of course are affected by the air we breathe.

Green cities are more pleasant

In the early twentieth century, people fled over-crowded cities for suburbs, or at least lower-density areas of the city, in part because of the poor environmental quality. While water quality in cities has significantly improved, and sewers are sanitary, and horses no longer befoul our streets, today still, air quality in cities is usually worse than in lower density areas.

Street Araber, c. 1976, Baltimore Maryland
Street Araber, c. 1976, Baltimore Maryland

Recent research by University of Minnesota colleagues reports:

Results: The proportion of physically active individuals was higher in high- versus low-walkability neighborhoods (24.9% vs. 12.5%); however, only a small proportion of the population was physically active, and between-neighborhood variability in estimated IHD mortality attributable to physical inactivity was modest (7 fewer IHD deaths/100,000/year in high- vs. low-walkability neighborhoods). Between-neighborhood differences in estimated IHD mortality from air pollution were comparable in magnitude (9 more IHD deaths/100,000/year for PM2.5 and 3 fewer IHD deaths for O3 in high- vs. low-walkability neighborhoods), suggesting that population health benefits from increased physical activity in high-walkability neighborhoods may be offset by adverse effects of air pollution exposure.

Over the coming decades however, hybrid-electric and electric vehicles are likely to be more common, if not the only vehicles allowed on city streets. The smell of the city will change. EV cities will be less polluted and much nicer, and thus more attractive than earlier polluted cities, or cities without such vehicle-type regulation. It will come a time that not only will cities be better for the global environment, resulting in less overall carbon emissions than lower density areas with greater distances and fewer shared walls, but they will be as good (if not better) for the individuals residing in them, with less overall pollution per capita and perhaps lower pollution intake than suburban areas.

Emissions, Equilibrium, and the $10 Bill

On February 1 (at 6:05 am) I found a BART card with $1.35 of money still on it on Sacramento Avenue near the North Berkeley BART station. I picked it up and used it. In economics there is the parable that you never find $10 bills on the ground, because someone would have picked it up already. And that of course is true in a steady state where no one ever drops another $10 bill. Eventually they will all be picked up. But if someone does drop a bill, it is on the ground until someone picks it up.

The most charitable view of emissions, and it doesn’t matter which pollutant (e.g. the EPA criteria NOx, SOx, VOC, CO, PM10, PM2.5, or even CO2, among others), is that nature has not yet adapted to take advantage of the changed environment. If we increase nitrogen in the air slightly, we expect life will evolve over time to be slightly more nitrogen-phillic somehow. Those gene-lines that manage this evolution survive, those that don’t die off. The problem of course for big slow species like large mammals, or trees, is that it takes a long time (many generations, hundreds, thousands, tens of thousands of years) to evolve in a way that is well-adapted to the new environment. So after a sudden change or shock, a species may find its way to a new equilibrium, assuming there are no other shocks or external changes to the system, or be beaten to its appropriate niche by some other species, and go extinct.

But life itself is a disequilibrating process. Humans (and a few other species) for instance invent “technologies” (from using sticks for digging, or rocks for breaking things, to fire or iPhones). These technologies change the environment for humans and other species. If we did that and stopped, an equilibrium could possibly be found. But we continue to invent.

Further, the earth itself is not a closed system. We are being continuously showered by radiation from the sun (you know, light and heat and all), (which we adapt to, assuming it is roughly constant). The earth is also periodically showered by the detritus of the universe (meteors and asteroids). These add to the disequilibrium we face, and are reputed to have done in the dinosaurs.

So it is one thing to say life will adapt to the changes in the environment humans create, undoubtedly some life will do better than others unless we manage to extinguish it all. The question is how long it takes to come to a steady state ( without any external shocks).

Should we privilege the “steady state” ante-Industrial Revolution vs some current or future “steady state”. That seems to me an entirely arbitrary preference. By restoring life to some elysian past we are condemning those species that evolved faster and co-evolved with our technology (from chickens and cows to pigeons and squirrels, among the larger life forms). To say this is the perfect end-state now diminishes possibilities yet to be.

What is our objective? Preservation of the existing mix of species, restoration of some past mixture, maximization of total biomass, maximization of human biomass? Unless people can agree on what it is we want to achieve, the means (pollute, don’t pollute) will remain unsolved. To say “Save the environment” begs the question of which “environment” we are trying to save.

However, if we think of this in property rights terms, we can either define the commons as unowned (which quickly degenerates to a bad outcome), or define it as owned by everyone, as if we are all shareholders in the commons, and the proxy is held by the government (or governments) (1).

In that case, individuals (and firms) have no inherent right to pollute (which we might define as measurably changing the chemical composition of the air (water, land) at some fixed distance, say 10m, at any rate some distance such that breathing does not count as pollution, but tailpipe emissions do). Instead of trying to geo-engineer an ideal world, which is beyond our abilities anyway, even if we could agree upon on it, we would regulate the inputs to that future world in the form of regulating pollution. Nature will then evolve to whatever it evolves to, with a minimal additional influence from humans. We might hope it turns out ok.

The transition from the present “environment as an unowned commons” into which we can dump anything to an “environment as communally owned property” into which we can dump nothing without permission or penalty will obviously be a difficult one. Many processes that were efficient in the absence of pollution prohibitions and penalties are inefficient in their presence. But crisis creates opportunity, and for every old-style industry and behavior the new regime obliterates, a new technology and way of operating arises.

This is the logical outcome of the <a href=”https://en.wikipedia.org/wiki/Enclosure”>enclosure movement</a>, which has been steadily assigning ownership to the unowned over the course of human history.


(1) We could have an alternative, where the environment is somehow owned by selected individuals instead of as a commons or by nobody, but carving up the air is much harder than carving up the land, since air moves much faster than earth.

Noise Walls and Pollution

With recent neighborhood opposition to noise walls, an interesting question arises related to the effects of noise walls on air pollution. Do roadside barriers protect the neighbors from tail-pipe pollutants? Does this result in more pollution on the roadway itself?

The answer, as with everything is that it depends.

Baldaufa et al. (2008) in Impacts of noise barriers on near-road air quality (Atmospheric Environment Volume 42, Issue 32, October 2008, Pages 7502–7507) write in their abstract:

Numerous health studies conducted worldwide suggest an increase in the occurrence of adverse health effects for populations living, working, or going to school near large roadways. A study was designed to assess traffic emission impacts on air quality near a heavily traveled highway. The portion of highway studied included a section of open field and a section with a noise barrier adjacent to the road. In addition, the section containing the noise barrier included a portion with vegetation in the vicinity of the barrier. Thus, this field study provided an opportunity to evaluate near-road air quality with no barriers, with a noise barrier only, and with a noise barrier and vegetation adjacent to the road. Pollutants measured under these scenarios included carbon monoxide (CO) and particulate matter (PM).

Measurements showed the effects of a noise barrier on near-road air quality. The presence of this structure often led to pollutant concentration reductions behind the barrier during meteorological conditions with winds directionally from the road. CO and PM number concentrations generally decreased between 15 and 50% behind the barrier. However, conditions occurred when pollutant concentrations were greater behind the barrier than when no barrier was present. These results imply that the presence of a noise barrier can lead to higher pollutant concentrations on the road during certain wind conditions. In addition, the study results suggested that the presence of mature trees in addition to the barrier further lowered PM number concentrations.

Emphasis added

Demand Side Solutions to Ice-Related Falls

I talked before about things we can do to reduce the iciness of sidewalks. That is a supply side solution. We need to think about demand side solutions to the problem of ice-related falls on icy sidewalks.
Bill Lindeke wants to turn it into a game, but in the end, he is still young.
There are things we can do to better accommodate the ice as well.

  • I can wear cleats of some kind or another. The problem is walking on non-ice, or worse cleared pavement, is not nearly so good with this tool. And ice is non-homogenously distributed across our sidewalks this time of year.
  • I can walk around with a hair dryer and a very large battery.
  • I can drive.
  • I can not travel on ice.

I like the last one best. Why TF am I walking around on ice? In the end, not all travel can be safely accomodated.
P.S. The number of my falls each year can probably be measured by the number of posts complaining about ice.

It’s Toasted

MaunaLoa
Global Warming needs an advertising campaign. While those trying to stop it are well-funded, and many organizations try to deny it or minimize its effects, almost no one is selling us on its merits. Global warming opponents make is seem like the earth is going to become a dried up desert-like husk. One of my friends insists it’s too late, the Earth is Toast.
Embrace that idea. Instead of the “Earth is toast”, we need to say It’s Toasted, giving the new and improved earth a warm and cozy feel, like a hot breakfast on a Winter’s Day. And every day, we are slightly more and more toasted.