Cascadia Scorecard Weblog

Chain of Evidence

From CNN, a story suggesting that Oregon's emphasis on pedestrian and bike-friendly cities has helped it keep obesity in check.

According to a study released Tuesday by the Washington, D.C.-based Trust for America's Health, the percentage of overweight Oregonians held steady at 21 percent last year, a sharp contrast to Alabama, where the rate of obesity increased 1.5 percentage points to 27.7 percent.

What makes Oregon different is its emphasis on urban design, which encourages outdoor activities like biking to work, the study's authors said.

Now, obviously, only a small share of Oregon residents walk or bike to work; and many people who do so have farily short commutes. But that's exactly the point:  when it comes to obesity, even a little bit of exercise can make a big difference.  On average, adults put on a pound or two a year -- but a pound of extra weight per year averages out to just 10 calories per day.  That's less than a teaspoon of sugar, or a daily stroll of about a tenth of a mile.  So even though Oregon cities' neighborhood design may have only a small effect on walking and biking, that effect could very well have been enough to keep Oregonians from putting on as much weight as Alabamans.  And by curtailing the growth of obesity, Oregon may have helped keep its citizens healthy, while stemming health care costs--which now account for about one out of every eight dollars Oregonians earn.  Which is one way of responding to people who question whether sidewalks and bike lanes are really worth the cost.

Obesity Grows

Obesity rates are growing in every state but Oregon, according to a new report by Trust for America's Health based on data from the CDC. (Read the Seattle Times article here.) While Oregonians can be proud of their accomplishment last year, they are not the trimmest state in the country, nor in the Northwest.

Interestingly, every Northwest state has lower rates of obesity than the national average. Montana residents are least likely to be obese; Alaskans are most likely. As Jessica pointed out recently, it's worth paying attention to obesity trends, not only because of their health consequences, but because it can absorb a lot of money.

Here's the skinny on obesity in the Northwest states...

Percent of state residents who are obese, 2004

	Percent of residents who are obese, 2004
Alaska	23.5
California	21.5
Idaho	20.9
Montana	19.1
Oregon	21.0
Washington	21.7
United States	24.5

Medical Cost of Obesity

The US national rate of obesity has doubled since 1990, so that in 2004, nearly one-quarter of Americans (23.1 percent) were classified as obese. Medical studies have established clear links from obesity to a variety of medical conditions, including type 2 diabetes, high blood pressure, cardiovascular disease, and others. Obesity is also costly: the increasing prevalence of obesity and costs of treating obesity-related diseases has helped to fuel the recent rise in medical spending. By one estimate, 27% of the cost increase from 1987 to 2001 was due to obesity.

The latest studies estimate that obesity alone costs the US around $75 billion annually, while while the added costs of treating conditions brought on by simply being overweight bring that share up to 9.1% of total US medical expenditures. On a regional level, obesity alone costs the Northwest over $2.3 billion dollars a year. That’s around 0.5% of our gross state product (see table below).

	1990 Obesity Rate	2004 Obesity Rate	Annual medical spending on obesity 2003 dollars (% of all med. spending)
US	11.6%	23.1%	$75,000 million (5.3%)
WA	9.4%	22.1%	$1330 million (5.4%)
OR	10.9%	21.2%	$781 million (5.7%)
ID	11.9%	20.8%	$227 million (5.3%)

On an individual level, obesity increases annual medical spending per person by 37.4%, or around $730 a year. And overweight increases spending per person by 14.5%, or $247 per year.

The medical cost of obesity is a meaningful drain on our economy, and the costs listed here are only the direct medical expenditures. Not included are the indirect costs of lost productivity, lower quality of life, or years of life lost due to obesity-related illnesses.

While obesity is caused by many factors, studies indicate that the built environment is one influence. Sprawling neighborhoods designed for driving everywhere--with few sidewalks, nearby desirable destinations, or a direct route to destinations--can discourage residents from walking or bicycling. One way to fight obesity (while improving our quality of life) could be to redesign the places we live.

For Clean Air, Work Downtown

In our ongoing quest to discover how land use and urban form links to human health effects, I recently stumbled across something odd. It's a 2000 study of vehicle emissions per household in Puget Sound, authored by Larry Frank. I wanted to find out if there is a connection between air pollution and urban density. According to this study, there is, but in a way I didn't expect.

It turns out that the strongest land-use correlate to low household emissions is not residential density, but job-site employment density. That is, from a statistical standpoint, it matters less whether you live on Capital Hill or the Sammamish Plateau than whether you work in downtown Seattle or Bothell. The difference, I suppose, is that downtown Seattle and other places with high employment density are well-served by transit and are generally easier to get to with lower vehicle emissions than more far-flung workplaces.

Interestingly--this is only interesting if you're a geek; otherwise skip to the next paragraph--the drop in household emissions does not observe a linear relationship with employment density. For the lowest three quartiles of employment density household emissions are about the same (they're a little higher in the lowest density quartile), but then they drop off sharply at the beginning of the highest density quartile. This suggests that there's a threshold of employment density--perhaps the density at which transit, carpooling, etc become viable--after which emissions drop quickly.

It's also interesting, I think, that in this study residential density is less strongly correlated with lower household emissions. There is still a correlation--higher residential densities meant less vehicle emissions--but the difference, while significant, was relatively minor.

One reason perhaps emerges in another set of correlations. This study found that households located in census tracts with high employment density, greater mixes of land-use, and greater street network density--in other words, places with many characteristics of city living--actually generate more vehicle trips and more vehicle trips with a cold engine (which produces a disproportionate share of tailpipe emissions). Probably, this is because there are more services and amenities nearby and there's less incentive to "chain" trips together as a typical suburban commuter might on the way to or from work. Even so, the higher density households produce fewer emissions simply because the trips are not as long as for households in lower densities.

There's a lesson here, maybe, for those of us interested in urban form as well as everyone who's interested in improving air quality. From a public health perspective, it may make more sense to concentrate jobs in dense nodes with good transit access than to worry about other land-use features. Maybe the best reform to reduce vehicle emissions is more office space downtown.

About the study: The study uses an exhaustive (heh, heh) methodology that calculates three types of emissions (NOx, CO, and VOC) that accounts not only for driving distance, but also for speed, travel time, and emissions from starting the car (adjusted for estimated engine temperature at start). Its findings are based on data from the Puget Sound Transportation Panel Travel Survey, which records travel for 1,700 households over a two-day period by giving each member of the household over 15 a diary for recording trips and their characteristics.

UPDATE 8/10/05: Here's a link to an abstract of the study. As far as I know, the full version is not online.

Waiting to Inhale

People who move to the suburbs may think they’re fleeing the polluted air of the city.  Of course, there’s a tradeoff: by living in low-density suburbs, they spend more time in their cars. And as it turns out, the air inside your car may be just about the dirtiest you’ll breathe all day.

Last year, researchers in Sydney, Australia released a study (pdf) that measured the levels of benzene (a carcinogen) and other volatile organic compounds (VOCs), as well as asthma-inducing nitrogen oxides, among people who commute by car, bus, train, bike and foot.

The verdict? Car commuters breathed the worst air, getting the highest doses of benzene and other VOCs. Even bus commuters were exposed to lower levels of VOCs than car commuters (though bus riders breathed higher levels of nitrogen dioxide). Train commuters had the least exposure overall, with cyclists and walkers coming in second-best.

One reason for the difference is that motorists are breathing exhaust, both from their own vehicles and from nearby traffic. As the authors of the Sydney study note, driving on congested freeways puts motorists in a "tunnel of pollutants." By contrast, other travel modes reduce ambient exposures: trains tend to run on isolated tracks, buses often take express lanes, walkers and bikers may travel on quieter streets.

The US census says that 87.9% of Americans commute by car, truck, or van, and the National Household Transportation Survey shows that people who live in sprawling suburbs spend about 68 minutes per day in their cars--about 50 percent more than people who live in more compact urban neighborhoods.

So, to some extent, if you want more fresh air it may be smarter to move closer to downtown, rather than farther away.

Collision Course II

Last week, I wrote a post detailing how much car crashes cost.  An alert reader asked some followup questions about how to reduce his risk:

Does a decrease in vehicle-miles translate to a decrease in injuries? Am I relatively safer on my bike? On the bus?

Here are some quick answers.  First:  the more you drive, the greater your chance of getting in a crash.  See, for example, this chart from a Victoria Transport Policy Institute analysis of car crashes in British Columbia:
The relationship is pretty close to linear.  So if you want to decrease your crash risk, the most obvious strategy is to arrange your life so you can drive less, if you can.  Of course, some roads are riskier than others -- and rural two-lane highways are among the riskiest.  Congested urban roads and streets tend to have more crashes per mile driven than average, but fewer fatalities -- slower speeds make crashes less deadly.  Which may be one reason why the risk of dying in a car crash is higher at the urban fringe than in center cities or inner-ring suburbs, and why sprawling cities are more dangerous than compact ones.

Next:  If you want to be safer, take transit.  Measured per passenger-mile, transit buses and commuter rail are about as safe as you can hope for; buses seem to be more than 10 times safer than cars for their occupants, while commuter rail is about 80 times safer.  (But both are more dangerous than cars for other occupants of the roads.)  I wish I could say that biking would make you safer, but it doesn't seem to; mile for mile, biking is about 10 times deadlier than driving. Exercise benefits may partially offset the increased crash risk.

It's a shame that biking is so risky in the US.  Biking fatalities are down, of course -- they fell by 27% between 1975 and 2001 -- but mostly because of a steep drop in cycling by children.  But in Germany, the exact opposite has happened:  the number of bike trips doubled between 1975 and 2000, while the number of bike fatalities dropped by 64%. The difference, according to some researchers, is that public policy in Germany has emphasized bike and pedestrian safety -- including infrastructure, traffic calming, traffic education, and traffic regulations -- while policies in the US tend to emphasize fast travel by car.

One side note--although traffic fatality rates in the US are among the highest in the developed world, US drivers aren't particularly unsafe, nor are the roads we drive on.  Measured per mile, our fatality risk is about average.  The real difference is that we drive much more than our counterparts in other nations--and all else being equal, more driving means more car crashes.

Collision Course

Car crashes kill about 700 Washington residents each year.  Now, remember, that's out of a population of over 6.1 million -- meaning that, on average, your chance of dying in a car crash this year is just over one in 10,000.  With odds that slim, are collisions really such a big deal?

As far as I can tell, yes.  Here's why.

First there's this:  car crashes skew young.  Surprisingly, motor vehicle accidents are the leading killer of Washingtonians between the ages of 1 and 44, reaching a peak between the ages of 15 and 24.  Similarly, for those before retirement age, traffic deaths are third leading cause of shortened lifespans, trailing only cancer and heart disease.  So the significance of traffic accidents to human health is far greater than the absolute numbers might suggest.

And then there's this:  For every traffic fatality, there are about 54 nonfatal traffic injuries and more than 200 collisions that cause no significant injury. And not only do those collisions take a toll in terms of pain and suffering, they're really costly.  According to the National Safety Council, you can get a pretty good estimate of the direct, out of pocket costs of traffic accidents by multiplying the number of traffic fatalities by $5.4 million dollars.  (They estimate that this figure will cover medical costs, lost wages, property damage, and other direct, out-of-pocket costs resulting from collisions.)  Using figures for 2002, that means that traffic accidents in the state of Washington were responsible for about $4 billion in direct economic costs.

But the real economic cost of collisions is probably even higher.  The Safety Council estimates that each traffic fatality results on about $1 million in out of pocket costs, and each nonfatal injury, an average of $45,000.  But these figures doesn't account for pain and suffering, or how much people would be willing to pay to avoid a car crash. 

Now, it's always a bit creepy--and a lot controversial--to assign a dollar value to death or injury.  But there's no question that people don't just consider medical costs and lost wages when they think about their own safety.  The Federal Highway Administration estimates that, based on how much people are willing to pay to avoid dying in a car crash, a traffic fatality costs about $3.4 million in 2004 dollars (the figure in the link, $2.6 million, is in 1994 dollars; I adjusted for inflation).  That figure is lower than that used by EPA, which assumes that people are willing to pay more than $6 million, on average, to avoid death. 

Using these higher figures, the cost of car crashes escalates.  Depending on the assumptions you use, the comprehensive cost of traffic collisions may top $8 billion annually, in Washington State alone.

Just by way of comparison, the Washington State Department of Transportation will spend about $1.7 billion per year (pdf link to budget document) over the next two years on highway maintenance, operations, and construction.  Obviously, the state DOT doesn't pay for all transportation expenses in the state.  But it seems pretty certain that traffic accidents are far costlier than the roads on which they occur.

Have It Your Weight

A look at the fast food industry--an important contributor to the emerging obesity epidemic--courtesy of MSNBC and Newsweek. The skinny (or not so skinny, as the case may be) is that fast food chains like Burger King are getting back to fundamentals: greasy, fat-laden food. Forget about low-fat sandwiches; BK's new strategy revolves around items like the Enormous Omellete Sandwich that tips the scales at 760 calories.

As it turns out "hard core" fast food consumers make up only 18 percent of the general US population, but represent 49 percent of the sales for fast food outlets. The target demographic? Men, 18- to 34-years-old, who don't much like their jobs. BK can safely play to its (ever-expanding) base with increasingly unhealthy menu items, because they can count on industry giant McDonald's taking the flak from what BK's CEO dubs "the nutrition Nazis."

Eat The Rich

Rich people are nearly as likely as poor people to be obese, according to new research at the University of Iowa. USA Today reports that three decades ago, the chance of having a ballooning waistline inversely correlated to having a ballooning paycheck. But that's changed now. 30 percent of all Americans are obsese--defined as being 30 pounds or more above a healthy weight--and there's little difference between Americans of different income levels.

In possibly related news, USA Today also reported that a pub in Pennsylvania now sells a $30 burger that tips the scales with 10.5 pounds of beef, 25 slices of cheese, and a cup-and-a-half of mayo, among other condiments.

And in further possibly related news, the New York Times reports that excessive doughnut consumption is bad for your health. It also wags a mildly reproving finger at the USDA's new and oddly ambiguous food pyramid. Both subjects dear to this blog's heart.   

Death by Traffic

What do the United States, Poland, Portugal, and Greece have in common?  Lots of deaths from automobile accidents.  The US ranked 27th out of 30 OECD nations in traffic deaths per capita in 2002 -- with 30th place (Greece) having the most deaths, and 1st (Turkey) having the fewest.   By contrast, Canada ranked 12th.

Now, it's not that the US has particularly bad drivers, or that our cars are particularly unsafe.  Mile for mile, our vehicle injury rate is right in the middle of the pack; and our vehicle fatality rate, adjusted for miles driven, is actually a smidge better than the OECD average.

Instead, the reason we have so many traffic deaths and injuries is simply that we drive a lot. Part of why that's so is that we're affluent (meaning that we can afford to buy lots of cars) and our gas is cheap.  But most of it has to do with the way our cities have grown.  Sprawling community design has pushed destinations farther apart, making a car a necessity for most trips.  And when you need to drive everywhere you go, you wind up taking on more risk than you'd bargained for.