July 27, 2009
Series Editor: Ian Parry
Managing Editor: Felicia Day
Assistant Editors: John Anderson and Adrienne Foerster
Welcome to the RFF Weekly Policy Commentary, which is meant to provide an easy way to learn about important policy issues related to environmental, natural resource, energy, urban, and public health problems.
This week, Maureen Cropper and Elizabeth Kopits examine the phenomenon of initially rising, then peaking, then declining traffic fatality rates as countries develop over time. Based on their empirical research, the authors discuss possible explanations for the downturn in fatalities, and the lessons for poor countries currently in the stage of rising accident risks.
During the summer commentaries will be posted once every two weeks
Declining Traffic Fatalities: Lessons for Developing Countries?
By Maureen Cropper and Elizabeth Kopits
As industrial countries have developed over time, there has been a clear, inverted U relation between the incidence of traffic fatalities and per-capita income (a similar pattern is often observed between pollution and per-capita income). The initial, positive association between fatality rates and development is straightforward—as motorization takes off, more pedestrians become exposed to the risk of being hit, while occupants of one vehicle are more likely to be involved in a collision as the number of other vehicles on the road rises. What causes the relation between the fatality rate and income to peak, and then trend downward, is more complex. It is due, in part, to a decline in pedestrian fatalities as pedestrians shift to either driving or riding in vehicles. Lowering the fatality rate, however, is likely to require deliberate, safety-focused policies. A better understanding of what has caused the rate to decline in developed countries could provide important lessons for the design of effective auto-safety polices in developing countries.
We examined traffic fatality patterns among 32 high-income countries using the International Road Traffic Accident Database (IRTAD). Between 1970 and 1999, total traffic fatalities declined by an average of 35 percent among these countries. The decline in fatalities was most dramatic for pedestrians and cyclists, for whom the average fatality rate (that is, fatalities per capita) fell some 60 percent, compared with a decline in vehicle occupant fatalities of 21 percent. These trends are even more striking given that vehicle kilometers traveled (VKT) increased by about 250 percent over the period. So, pedestrian fatalities per VKT declined 86 percent on average, while occupant fatalities per VKT declined by 76 percent.
Explaining the Trends
To understand why these trends occurred, we began by examining the relationship between fatalities and per-capita income. A striking fact is that although pedestrian fatalities per capita and per VKT declined as per-capita income increased within these countries, there was no significant relationship between occupant fatalities and per-capita income. This suggests that reductions in occupant fatalities do not automatically accompany increases in income. What, then, does explain the decline in occupant fatality risk? To answer this question we examined, in addition to income, the impact of demographic factors, the number of motor vehicles and length of roads, a measure of alcohol abuse, and the availability of medical services on occupant and pedestrian fatality risks.
Demographic factors appear to be especially important: young drivers are likely to be less skilled, less experienced, and less averse to risk, while older drivers have more experience and perhaps drive more carefully (though an offsetting factor is that they may have a slower reaction time to an imminent collision). In fact, we found strong evidence that the share of drivers under the age of 24, which declined by 20 to 40 percent between 1970 and 1999, was positively associated with occupant fatality risk. This demographic trend alone could account for nearly 30 percent of the decline in occupant fatalities. We also found that the decrease in the share of drivers under age 24 reduced pedestrian fatality risk. On the other hand, an increase in the share of drivers aged 65 and over significantly raised pedestrians’ fatality risk, as did the share of the population living in urban areas.
Rising vehicle ownership rates affect fatality risk in a variety of ways. Occupant fatality rates per VKT initially increase as more vehicles on the road raise accident frequencies. However, the faster the fleet grows, the higher the proportion of recent models equipped with advanced safety features, which causes the occupant fatality rate per VKT to decline. Initially, pedestrian fatality rates rise as motorization takes off, although this trend peaks and then reverses as the share of pedestrian trips in total travel trips declines.
Expanding the total capacity of the road system over time (for a given vehicle fleet size) reduces occupant fatality risk, as collisions are less frequent when cars have more space. The effect is especially pronounced for pedestrians, perhaps because larger road networks include more motorways that separate vehicles from foot traffic. However, road improvements (additional and wider lanes, for example) may encourage more risky driving behavior, leading to an increase in collision frequency, offsetting the benefits of better roadways.
Elizabeth Kopits is the senior economist for energy, environment, and natural resources, at the President’s Council of Economic Advisors. She is on leave from the National Center for Environmental Economics at EPA and is a former RFF research assistant.
Alcohol abuse (as proxied by a country’s incidence of liver disease) is positively correlated with occupant deaths per VKT. Over the study period, the liver-disease death rate decreased substantially (by 30 to 60 percent) in the United States and many European countries. These reductions in alcohol abuse contributed to about a 6 percent decline in occupants’ fatality rates. Alcohol abuse has an effect that is twice as large for pedestrians as for vehicle occupants, likely reflecting not only drunk driving but also risky behavior by pedestrians under the influence. Changes in alcohol use contributed to nearly a 10 percent decline in pedestrian deaths per VKT.
Finally, increases in the availability of emergency medical care services (as measured by physicians per capita) significantly decreased occupants’ fatality risk, but had no statistically significant effect on pedestrians’ fatality risk. No matter how quickly accident victims are rushed to the hospital, it seems, the likelihood of death is higher for pedestrians than for vehicle occupants.
Our study was limited to 32 high-income countries for which we had reliable data. We believe, however, that the findings are relevant to developing countries, whose per-capita incomes today are comparable to those of the poorest IRTAD countries 40 years ago. Their patterns of traffic fatalities—in particular, the high rate of pedestrian fatalities—also recall the former situation for industrialized countries.
The decline in the road death rate in industrialized countries is attributable largely to a decline in pedestrians’ death rate. It appears that this decline is due to increased motorization and a smaller proportion of young drivers. The factors that best explain the decline in occupant fatalities per VKT are reductions in alcohol abuse, improved medical services, and a shrinking of the young driver population.
Reductions in alcohol abuse and improved medical services are clearly the result of explicit resource allocation decisions. The importance of the demographic factor suggests that in countries where young people constitute an increasing share of the driving population, policies to improve young driver education and reduce speeds will be crucial.
Kopits, Elizabeth and Maureen Cropper. 2008. Why Have Traffic Fatalities Declined in Industrialized Countries? Implications for Pedestrians and Vehicle Journal of Transport Economics and Policy 42(1): 129–154.
Kopits, Elizabeth and Maureen Cropper. 2005. Traffic Fatalities and Economic Growth. Accident Analysis and Prevention 37(1): 169–178.
Noland, Robert. 2003. Medical Treatment and Traffic Fatality Reductions in Industrialized
Noland, Robert. 2003. Traffic Fatalities and Injuries: the Effect of Changes in
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