‘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. You can leave a response, or trackback from your own site.

14 Responses to “‘Portion Distortion’ and the American Road”

  1. Fritz Says:

    What I want to know is: are radar guns like that available for anybody to buy?

  2. Tom Vanderbilt Says:

    Well, since you asked: Oh, and by the way, the tuning forks are a very old school calibration device, and are less than accurate, or so I’m told.

  3. Brigitte Says:

    Vancouver, British Columbia, is a good example of a North American city with rather narrow streets. In Montreal, residential streets of the same width are one-way, and cars zoom down them. In Vancouver, residential avenues (numbered) are “narrow” (i.e. three-lane wide, including parking on each side and one travel lane in the middle, still much wider than in many European towns) but two-way. The result in Vancouver is that drivers have to go much more slowly and be prepared to “duck” into a parking spot to let another car go by… or in some (rare) situations back off. Much less efficient, much more humane.

  4. Carice Says:

    Great post!

  5. Jack Says:

    This video is not surprising to me at all. I witness speeding cars (usually 20 mph over 30 mph posted) and red light runners daily, all in front of a police substation. Every intersection around our neighborhood has the same problems, but worse. Maybe I should get one of those cameras too.

    No doubt our eyes are bigger than our stomachs and our driving habits have gotten worse with the growth in convenience foods. Until we have effective and fair law enforcement, our streets will remain dangerous. I agree, “it is much easier to change a person’s environment than to change their thinking”.

  6. Dave Says:

    This is something I’ve thought a lot about. Living in Portland, Oregon, there are plenty of very narrow streets where, especially if there are cars parked on the side, one person has to pull over to let another person by. This keeps speeds of traffic often down even below 20mph – of course there are also main roads where there is nothing to stop a car from going 55mph except occasional stoplights (speed limits are very rarely enforced anywhere in the city). Any guesses where there are more accidents?

    In thinking a lot about infrastructure both here and in the average European city, I think density plays a huge role. In Amsterdam, for instance, the density of people in the city simply means that a person cannot drive 55mph safely in the city, there isn’t room for roads that would support that.

    In Vilnius, Lithuania, I felt very safe as a pedestrian, because streets were small, often cobbled, and therefore traffic speeds were pretty moderate within the city (of course, there are always some exceptions). Most people used public transit because it went literally everywhere, and was much cheaper than owning/driving a car.

    From personal experience, I would agree with the assertion that the faster you go, the harder it is to judge how fast you’re moving. Even in our 1974 VW Beetle, the feeling of going 70mph is not proportionately different than going 35mph – not to mention in cars that are made for going fast. You can be going 100mph and have it feel like you’re just cruising along.

  7. Cheryl Says:

    It should be considered a product defect to manufacture cars which can speed. Since we can’t depend on drivers to drive safely in cars built for speed, perhaps cars which CAN’T speed are the answer – smart roads and cars which share info and prevent cars from accelerating over the speed limit. I know – overkill of technology – but failsafe. Do the speed cameras in Britain improve road safety? I’ve read that they don’t, but don’t really trust the source.

  8. Eric McClure Says:

    Tom, thanks for posting about and linking to our video.

    You and Brian Wansink are exactly right about excess road capacity and its inducement to speeding, something that was borne out in a road-test experiment.

    We conducted a road test under controlled conditions to see how long it takes to drive (at the legal speed limit) from Union Street to 15th Street via both Prospect Park West and 6th Avenue, and from 15th Street to Union Street via 8th Avenue and 6th Avenue, in order to compare these one-way avenues with a neighborhood two-way avenue. We conducted the test at night to control for traffic volume (we were able to travel unimpeded by other vehicles); we made sure we started from a red light as the first vehicle each time; and we accelerated normally and used cruise control in order to maintain the 30-mile-per-hour speed limit when not braking for a red traffic light. The southbound trip took exactly two minutes and 57 seconds on both Prospect Park West and 6th Avenue. The northbound trip took three minutes and 20 seconds on 8th Avenue, and three minutes and 40 seconds on 6th Avenue. We repeated the drives in order to make sure conditions were consistent.

    What can’t be quantified, but was clearly something we experienced, was that it felt like we were poking along while maintaining the speed limit on three-lane, one-way Prospect Park West, and conversely, it felt like we were speeding recklessly while driving at the speed limit on two-lane, two-way Sixth Avenue.

    It was clear confirmation that street design and capacity plays a large role when it comes to speeding.

    Keep up your great work!

  9. azbikelaw Says:

    “A separated bike lane would be a great place to start — and would reduce the frequent cases of cyclists using the adjacent sidewalk”

    I’m not sure what is meant by separated, but unless the (usually many, many) intersections can be somehow managed, these sorts of bike paths tend to have worse safety problems.

    In other words, what you gain in reducing side-swipe and rear-end collisions are more that offset by an increase in turning/crossing collisions. (the separation tends to take cyclists out of the line-of-sight of motorists… out of sight out of mind!).

    Being struck from behind, particularly in an urban (versus rural) environment and with a properly lighted cyclist, is a relatively rare mode of collision. This is hard for many to accept; but it has always and repeatedly been proven true, see e.g. Cross and Fisher

  10. azbikelaw Says:

    I, too, would be interested in the Britian – speed camera vs. safety linkage.
    In your book, you said something about how over the 1990’s british safety stats improved markedly (and sort of implied it was caused by the cameras). I didn’t see any footnotes for that but maybe i missed it. Anyways I think that would be a great topic for fleshing out.

    There was a WSJ op-ed today pooh-poohing the notion of cameras causing a safety improvement. His comment on Britain was that “Britain has gone furthest in using cameras for comprehensive auto surveillance”, and NOTHING about safety !? see no evil, hear no evil , speak no evil.

  11. anonymouse Says:

    azbikelaw: in this particular case, there are no intersections because the bike lane would run along the park. Almost all the intersections on Prospect Park West are T-intersections because of the park, and the bike lane will probably be on the park side.

  12. Rational Plan Says:

    The link between speed cameras and accident prevention has proved controversial in the UK. Mainly because accidents had started to decline long before their wide spread introduction and and have now that accident levels are not reducing any more despite the massive increase in camera fines. Partly this is because the increase in cameras has seen a dramatic fall in traffic police patrols, corresponding with an increase in accidents from run red lights and the increase in accidents of people who have no licence and are therefore uninsured.

    A much bigger roll in the reduction in accidents in the UK is use of local road building funds primarily for road safety and junction redesign. Each council has a rolling target of accident reduction and it has to outline a plan how is it going to do it. For example the council where I live has just designated a neighbourhood near me a 20 mph zone. The old speed bumps were replaced, with humps that slowed cars but not buses, new speed tables plus junction narrowings. It is much more natural to drive at a slower speed. It is rare these days to find a residential road that is not subject to built in speed restrictions.

  13. Kelley Says:

    Good news: the road diet is on its way!

  14. Alan Says:

    Pittsburgh, too, has very narrow streets, with much of it being cleverly jammed onto hillsides and into valleys. I definitely see cars pulling to the side to let others pass on a regular basis on the side streets.

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