‘Portion Distortion’ and the American Road

I’ve recently been reading a number of papers by Brian Wansink, director of the Cornell Food and Brand Lab at Cornell University, and author of Mindless Eating.

One of Wansink’s more interesting findings is that the way food is served to us affects how much of it we will eat. He calls this “portion distortion.” Not only does the size of the portion itself affect how much we will eat, but so too does the size of the container it comes on (or in).

This seems to happen even to highly educated health professionals; in one study, he found they ate 31% more ice cream when it was served to them in a larger bowl (with a larger spoon, their consumption went up by more than 12%). In another experiment, people given larger containers of popcorn in a theater ate more than those given smaller containers — even when the popcorn was stale (though the affect was reduced when the popcorn wasn’t fresh — i.e. larger containers boosted consumption by 45.3% with fresh popcorn, and by 33.6% when it was stale). This effect typically seems to happen without people being aware of it.

It’s not difficult to imagine the public health consequences of this, particularly as the American obesity epidemic seems to roughly track a number of changes Wansink has identified in portion size. To wit:

We find portion distortions in supermarkets, where the number of larger sizes has increased 10-fold between 1970 and 2000. We find portion distortions in restaurants, where the jumbo-sized portions are consistently 250% larger than the regular portion. We even find portion distortions in our homes, where the sizes of our bowls and glasses have steadily increased and where the surface area of the averaged dinner plate has increased 36% since 1960. And if our bowls, glasses, and plates do not distort us, our recipes will. In the 2006 edition of the Joy of Cooking, the serving size of some entrées has increased by as much as 62% from some recipes in the first edition of 1920.

One problem (there are others), Wansink suggests, is that the feedback loops begin to fray with larger portion size: The larger the portion size, the less accurate the estimation of calories consumed becomes.

What does this have to do with the road? There is an interesting story in how the rise in portion size — often associated (as Wansink notes) with fast-food restaurants — historically tracks the huge increase in miles traveled (183% growth in per-person miles from 1969 to 2000, a period in which the number of persons itself increased only 41%), which itself is associated with the rise of those same restaurants; not to mention the much-debated work linking obesity to density and travel modes.

But I had a different comparison in mind: The way the size of our roads affects our behavior in “consuming” them as drivers. This was brought home to me again in a recent video made by a group called Park Slope Neighbors, which is working to reduce the size of streets like Brooklyn’s Prospect Park West (a five-lane thoroughfare, two lanes of which are dedicated to parking). As the video below shows, the speeds on the street are routinely in excess of the 30 MPH limit. What makes this particularly worrisome is that across PPW lies Prospect Park itself, and there is thus a steady march of pedestrians (including many children). I’m often struck as a driver by how many people are blowing past me; and, just from personal experience, I see more red-light running on this street than others in NYC.

The one thing I rarely see on PPW is the street used to its full capacity by cars. So in the 90% of the time it’s not hitting that full peak (my own wildly rough estimate, NYC DOT, please feel free to weigh in with actual numbers!), it is treated more like an urban highway, with speeds of 45 (or higher) mph not uncommon.

When I took my U.K. driver’s test in the suburb of Pinner, near London, I was intrigued by how, on several local roads, I often had to pull over to let another driver past, so narrow were the residential streets. This is something I can’t remember ever having had to do at home. In the U.S., talk of narrowing roads often leads to the reflexive question “What about emergency response?” Somehow, England manages to have these roads without suffering from a rash of people dying in house fires (needless to say their traffic safety record is better as well; as a friend who did some consulting for the Department for Transport recently told me, somewhat amazed, ‘they actually seem to really care about reducing the number of people killed on the roads’).

One of the recommendations for Prospect Park West is to put it on a “road diet,” a deeply suggestive phrase in light of Wansink’s research. A separated bike lane would be a great place to start — and would reduce the frequent cases of cyclists using the adjacent sidewalk. But something has to be done to change the context of the street. Underutilized by cars much of the time, it is an inefficient use of urban space, and its capaciousness sends a set of powerful signals to the driver, more powerful than whatever speed limit signs may be present. It represents, to paraphrase Wansink, “mindless speeding.” People drive fast because it feels like they should. They see a wide road, and don’t give themselves much time to see anything else.

And to return to that notion of feedback loops. Wansink noted that with larger portion sizes people became less well adept at judging their calorie consumption; I haven’t seen this study (or maybe I have and have forgotten), but I suspect that the higher speed at which one drives, the less able one is to accurately judge one’s speed. Just a theory.

Sure, we could post yet more signage. We could put increased police patrols along the way. We could run expensive ads showing people what happens to pedestrians when struck by vehicles at 20 mph versus 30 mph. But as Wansink writes, in the context of eating, “it is much easier to change a person’s environment than to change their thinking.”

This entry was posted on Tuesday, April 14th, 2009 at 3:58 pm and is filed under Drivers, Roads, Traffic Engineering, Traffic safety, Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.

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