CDC Epidemiologist "Misses the Point" on Averting Traffic Deaths

Responding to an article in the New York Times Science section this past week, New Haven-based author and urbanist Phil Langdon published the following op-ed on the New Urban Network.

Langdon argues that public health professionals need to pay more attention to road design if they want to have any meaningful impact on reducing the 40,000 traffic deaths each year in the United States.

Though this point was made by a recent CDC report outlining methods that will work to reduce obesity in the United States, it apparently hasn't filtered its way down to epidemiologists and journalists who study traffic fatalities. The article, which originally appeared here, is reprinted with permission of the author.

Missing the point on how to avert traffic deaths

Motor vehicle accidents cost the US $99 billion a year, or roughly $500 for each licensed driver, The New York Times reported Aug. 31 in its Science Times section.

That includes $17 billion in direct medical expenses and much more in lost wages, productivity, and disability, The Times said, attributing the figure to Rebecca B. Naumann, lead author of a study by epidemiologists at the Centers for Disease Control and Prevention.

In a country where the automotive way of life often goes unquestioned, it’s useful to be reminded of the horrendous toll inflicted by motor vehicle crashes.

“Teenagers and young adults, who represent only 14 percent of the population, account for almost one-third of injuries and fatalities and almost one-third of the costs,” reports Roni Caryn Rabin. “Pedestrians and motorcyclists, who represent 11 percent of the injuries, rack up 22 percent of total costs, because of the severity of their injuries,” she says, noting that the study first appeared in the journal Traffic Injury Prevention.

But what are we to make of the final paragraph in the Times article? It states: Among the interventions proven to reduce the toll are strict seat-belt laws, more enforcement of speeding laws, educating parents about child safety seats and using devices that lock out drivers who have been drinking alcohol, Ms. Naumann said. Policies that restrict inexperienced teenage drivers also significantly reduce crashes, she said.

The report makes no acknowledgement of the impact of faulty design of the nation’s streets, roads, and communities. It seems strange that an epidemiologist at the CDC — which recently has shown a strong interest in the effects of community design — would not point out the role played by roadways that practically invite motorists to speed.

Planning consultant Peter Swift and others, in a study that was first presented to the Congress for New Urbanism in 1997, amplified in 2002, and amplified again in 2006, identified an important reason for serious traffic accidents: Many residential streets are too wide.

After studying the conditions under which nearly 20,000 accidents occurred over eight years in Longmont, Colorado, Swift and his co-authors came to an unambiguous conclusion: “narrow streets are safer.” They declared: “Clear relationships are evident between accident frequency and street width. The findings support the premise that narrower, so called ‘skinny’ streets, are safer than standard width local streets.”

If you build narrower streets and provide them with a sense of enclosure (by planting lines of street trees, allowing cars to be parked on the streets, and perhaps bringing houses and other structures closer to the roadway), most drivers will naturally slow down. The physical environment can be richly outfitted with objects and dimensions that result in fewer life-threatening crashes. In the Longmont study, the difference between a typical 36-foot-wide residential street and a 24-foot-wide street was found to be “a 487 percent increase in accident rates.”

Speed is a critical factor in whether a person who is hit by a car will live or die. “A pedestrian has a 5 percent chance of being killed at 20 mph,” Norman Garrick, a transportation specialist at the University of Connecticut, told New Urban News in an article published in January 2007. At 40 mph, the pedestrian has “an 85 percent chance of being killed.”

Another key to reducing traffic injuries and deaths: Give people opportunities to drive less, in part by developing extensively connected street networks. Todd Litman, in a 1999 study for the Victoria Transport Policy Institute, recommended laying out neighborhoods so that they have a grid-like organization of narrow streets with short blocks, many T intersections, and other devices that cause motorists to proceed more slowly and that make it possible to go places without even getting in a car.

When there is a grid of streets, people can reach destinations with shorter drives — and in some cases they can travel by bicycle or on foot, which is better for them in many respects. When the streets are properly designed, the environment will be comparatively safe. A generously connected, relatively slow-paced circulation system is a far cry from the more typical suburban practice of funneling traffic from cul-de-sacs onto collector roads and then onto large arteries, requiring people to go long distances, at higher speeds, to reach stores, schools, and other elements of daily life.

Garrick and fellow transportation researcher Wesley Marshall analyzed the facts surrounding more than 130,000 vehicular crashes in California cities and discovered that the communities built since 1950 had the worst traffic fatality rates. As reported in New Urban News in January 2009, the post-1950 cities tend to have more branching, tree-like street networks that include many cul-de-sacs and not many intersections. This limits the movement of traffic through residential areas but forces people to travel longer distances, ultimately exposing them to higher speeds and greater danger.

A report from Europe has found that when average vehicle speeds drop by just 5 percent, the number of injuries drops by 10 percent and the number of fatalities falls 20 percent. Extensively connected street networks may not have fewer crashes over all, but the crashes that occur are less likely to leave someone dead.

Finally, “Dangerous by Design,” a study released in November 2009 by the advocacy group Transportation for America, found that during the previous 15 years more than 76,000 pedestrians were killed. Most of the deaths, 56 percent, occurred on arterial roads — focal points for sprawl, often combining substantial width, high traffic speeds, and few or no facilities for pedestrians.

It is odd that an epidemiological team at the CDC would fail to beat the drum about these factors, and would instead emphasize interventions such as greater enforcement of speeding laws. Does anyone really believe that ticketing speeders is going to bring about lasting change in how fast traffic moves? How can that be, when so many roads are designed to facilitate speeds that cause accidents to be lethal?

The fact is, others in the CDC have become intensely aware of the effects of community design on health and safety. A number of CDC personnel participated in the Congress for New Urbanism conference in Atlanta last May, which looked at the connections between community and physical and mental health. The effect of community design on Americans’ well-being has also become a focus of the Robert Wood Johnson Foundation, a major financial supporter of health initiatives.

Granted, interventions in community design may take longer to carry out than programs aimed at enforcing seat-belt laws, educating parents about child safety seats, or handing out speeding tickets. Unlike enforcement of speed laws, they don’t produce an immediate payback for government through tickets and fines.

Nonetheless, changing the physical environment has to be at the core of any campaign to avert traffic injuries and death. Change the physical environment, and you alter behavior — not just for a few months but for years to come.

To judge from the story in The Times, not enough people in either the health fields or in journalism are aware of how much can be accomplished by more intelligently designing America’s streets, roads, and communities. We have some serious educational work yet to do.

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Also see: New Study: 20MPH zones greatly reduce injuries and fatalities