Vanishing Automobile Update #22

Fake CDC Study Full of Holes

Several newspapers and other news sources have recently reported that a study published by the Centers for Disease Control (CDC) has warned about the health dangers of living in the suburbs. Public health officials, the study says, must support smart growth in order to promote a healthy, productive population.

In fact, the study is NOT a CDC report and was probably written without the official endorsement or even knowledge of the CDC. Instead, the report, which is titled "Creating a Healthy Environment: The Impact of the Built Environment on Public Health," was published by SprawlWatch Clearinghouse, a smart-growth group.

The report lists the authors as Dr. Richard Jackson and Chris Kochtitzky, both of whom work for the CDC. The report's cover prominently displays the words "Centers for Disease Control and Prevention" underneath the author's names. While this indicates their affiliation, many news sources have misconstrued it to mean that CDC published the report. The report's true publisher, SprawlWatch, has done nothing to correct this error and has obviously enjoyed a great media success.

Of the two authors, one is primarily an urban planner who works for CDC as an associate director for policy and planning. The other is a medical doctor who works for CDC in an administrative capacity.

These two people may have written the report with the best of intentions. But the report is as unscientific as anything ever published by smart-growth groups. It is full of logical fallacies and inconsistencies. Most important, it fails to document any of its claims.

The report's thesis is that suburbs are a public health menace and that smart-growth is the public health solution. The report's fundamental fallacy is the old "design myth" held dear by many architects and urban planners. This is the myth that "we shape our cities and then our cities shape us," in other words, that urban design determines how we live and that better design can make us live better.

The specific claims made in the report are that:

  1. Suburban sprawl leads to more toxic air pollution. But the report cites no evidence that this is true. In fact, dense, congested cities contain more air pollution hazards than the suburbs.
  2. Suburban sprawl leads to obesity. But the report cites no evidence that this is true. In fact, rising incomes are more responsible for obesity and changing exercise habits.
  3. Suburban sprawl is dangerous for pedestrians and bicyclists. But the report cites no evidence that this is true. In fact, the high traffic levels in congested cities are much more dangerous for pedestrians and bicyclists than the suburbs.
  4. Suburban sprawl is dangerous for elderly and disabled people. Again, the report fails to tie the mobility problems of elderly and disabled people to the suburbs. There is no reason to think that smart growth is needed to solve these problems.
  5. Suburban sprawl is bad for water quality.

None of these claims are proven in the report and mainly are easily falsified.

1. The health effects of air pollution are a function of how many miles people drive, the congested conditions in which they drive, and the concentration of driving and pollution. The report points out that suburbanites tend to drive more than city dwellers and so concludes that suburbs lead to more toxic air pollution.

In fact, differences in driving between the suburbs and the cities are in large part attributable to differences in family size, income, and other factors. Forcing suburban families to live in smart-growth densities will not necessary reduce their driving.

More important, the other two factors affecting air pollution -- congestion and concentration -- are much worse in cities than in suburbs. To minimize the health risks of air pollution, we would be much better off moving the residents of dense cities to low-density suburbs than in densifying the suburbs.

In practice, air pollution is declining not because of changes in urban form but because of improved technology. The best way to reduce air pollution is at the tailpipe, not the ignition key. Although Americans drive three times as much today as they did in 1970, total automotive pollution is roughly two-thirds less than it was in 1970. Further improvements are easily possible at modest cost.

2. Obesity is getting worse in the U.S., says the report, and suburbs are the cause. While the report cites statistics indicating that Americans walked or bicycled more in the past than they do today, it fails to show that these changes are in any way due to suburban environments.

In fact, increases in auto driving are largely due to increases in incomes. Government policies aimed at increasing poverty in America will do more to increase walking and cycling than policies aimed at reshaping the suburbs. While few would seriously propose such policies, the reality is that the anti-auto, anti-suburb policies promoted by SprawlWatch and this report in particular will help to impoverish many Americans. This is simply due to the fact that automobiles have given people access to better jobs, and without autos people's incomes will decline.

3. Pedestrians and bicyclists, says the report, suffer from 13 percent of all traffic fatalities. However, the report makes no attempt to record what share of pedestrian fatalities is in the suburbs vs. in the cities.

The report does note that there are "strong associations" between "the risk for pedestrian injuries and high traffic volume." While many suburban highways have high traffic volume, these roads tend to have wide lanes and are often paralleled by low-trafficked routes. By comparison, the streets in dense cities tend to have narrow shoulders for bicycles, poor alternate routes, and pose high risks for pedestrians.

The report particularly focuses on the dangers of the suburbs to children, again without citing any data. Local suburban streets tend to be broad and, since most people park in garages or driveways, clear of parked cars. This gives motorists a clear view of children or others in the streets. In contrast, most urban streets are clogged with parked cars, creating a dangerous situation for children who may dash out between to parked cars in front of moving vehicles.

"The risk for injury to children living in neighborhoods with the highest traffic volumes was 13 times that of children living in the least-busy areas," the report says. This clearly argues for more suburban neighborhoods, where traffic volumes are low, rather than for urban neighborhoods. Yet the writers somehow draw the opposite conclusion.

4. Elderly and disabled people do suffer from mobility problems. Many of these people choose to live in neighborhoods that are designed to alleviate these problems. The report focuses on the fact that some neighborhoods lack curb cuts for wheelchairs or bus shelters for bus stops. While some of these barriers can be easily eliminated, there is no reason to think that applying smart growth -- high-density housing, mixed-use developments, high-density transit service -- throughout the suburbs is either necessary or sufficient to address the mobility problems of the elderly and disabled.

5. "Uncontrolled growth" is supposed to be detrimental for water quality, says the report. "In urbanized areas, rainfall that once filtered slowly downhill becomes surface runoff. It flows across compacted earth and impervious man-made surfaces." This changes water flows and means that pollutants directly enter streams rather than being filtered by the soil.

All of these things are true. Yet once again the claim that suburbs are the problem is wrong. Cities have a much higher percentage of impervious surface than the suburbs. The percentage of land covered by streets in auto-oriented suburbs tends to be at least a third less than the share of cities built before the auto. Suburbs with homes on half-acre lots have much larger areas of pervious grass and soil than urban apartments or homes on one-eighth or one-sixteenth acre lots.

As salmon biologists have realized in the Pacific Northwest, the solution to water quality problems is low-density development -- "sprawl" -- not smart growth.

In addition to the above issues, the report briefly mentions other public health problems supposedly caused by the suburbs. In almost every case, the real problem is in dense inner cities, not the suburbs.

In short, the report fails to show that any of the problems it attributes to the suburbs are really caused by the suburbs. In most cases, if the problems are caused by urban form at all, they are more due to dense cities than low-density suburbs.

Yet the report concludes that public health officials should become active in urban planning and provide planners "with the public health arguments they need to support 'smart-growth' designs and initiatives."

It is one thing for public health officials to encourage people to exercise more. Where evidence shows that sidewalks are safer for pedestrians, it may also make sense for public health officials to encourage sidewalks. But it is quite another thing for public health officials to make a wholesale endorsement of smart growth based on murky and undocumented claims that it is safer than low-density suburban development.

Smart-growth opponents should make certain that local news sources and public health officials understand that:

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