In this report there is a survey of statistical methods used by other researchers and what variables they have used as a measure of the state of the market. The most common variables were unemployment and a measure of the industrial production such as the gross national product (GNP). Unemployment, GNP/capita and the net increase of private cars were added to a model developed at VTI by Ulf Brüde, which uses time and vehicle mileage as explanatory variables to the number of traffic fatalities. The number of new private cars can be assumed to depend on the state of the market and should also have a connection to the number of new and inexperienced drivers that enter the traffic during a year. Unemployment turned out to be the most appropriate economic explanatory variable. An increase of unemployment seemed to indicate a decrease in the number of traffic fatalities. Unemployment has no reasonable direct impact on traffic safety but is connected to the hypotheses that economic demand drops in a recession or that the unemployment among younger people increases more than for the population as a whole. The former suggests that there are fewer heavy goods vehicles on the roads and accidents where heavy goods vehicles are involved often give dire consequences. The latter suggests that younger people, that are more prone to accidents, will reduce their car driving. Estimates of the annual mileage for heavy goods vehicles and younger people were included together with unemployment in a model for the number of road fatalities in Sweden between1981–2008. The mileage for heavy goods vehicles was not included in the final model, but the decrease of the number of road fatalities during the 1990s coincided with a large decrease in the mileage for younger people. Younger people almost halved their mileage compared to the late 1980s. A model proposed by Örjan Hallberg, that only uses the number of new cars as a proxy for the number of new drivers, also indicated that a part of the reduction in road fatalities in recent years is explained by a lower share of inexperienced car drivers among the road users. Another type of hypotheses is that the state of the market to some extent affects the behaviour and travel patterns of the road users. Data from fatal accidents between December-March 2008/2009 that was a time of recession, were compared to the same period 2005/2006, 2006/2007 and 2008/2009 when the state of the market was better. The only significant difference was that the number of people involved in a fatal accident was higher during the good economic periods (this was strengthened by two accidents involving buses). On the other hand it was not possible to establish, for example, that there were differences in when during the day the fatal accidents occurred or if they happened in weekdays or weekends. Such differences would have supported a hypothesis that there is more travel outside working hours in good economic times. It has been proposed that good economic times may induce a higher level of stress in society. Accordingly the same fatal accidents were also compared with risk-taking behavior of the involved drivers such as suspected speeding, non-use of the seat belt, driving while tired or under influence of drugs or alcohol. Another risk-taking behavior that might have a connection to the state of the market is driving without a valid driving license or using tires that are illegal or inappropriate on winter roads. None of these behaviors showed a significant difference in the share of fatal accidents where they were manifested. The comparison thus seems to indicate that both the “normal” fatal accidents and those where a risk-taking behavior was present decreased to the same extent in the recession period. The only exception was the number of suspected suicides, which was constant or even slightly higher in the recession period, so that their share of the traffic fatalities became higher than in the periods of good economy. This study confirmed the result from earlier studies where most researchers found that the number of road fatalities seems to decrease in a recession period. A part of the reduction of road fatalities in the long run was explained by the fact that younger people reduce their car driving, particularly during the recession in the early 1990s. There is still an effect of unemployment that is not explained in this study. An attempt to compare fatal accidents where some drivers had displayed inappropriate traffic behavior during a recession showed a sometimes unexpected similarity to the fatal accidents before the recession. For example, the share of fatal accidents involving suspected speeding or a drug impaired driver was about 20 per cent in both the recession and the period before. In absolute numbers, it thus seems that some risk-taking drivers may have dropped out of the traffic in the recession period. Why the number of fatal accidents with more careful drivers decreased by a similar amount, in a relative sense, is unclear. A more detailed study of how travel habits vary with the state of the market may give new ideas for further research. New insight may also be gained from collaboration with neighboring countries to obtain a larger common data material to study. (Author/publisher) This report may be accessed by Internet users at http://www.vti.se/EPiBrowser/Publikationer%20-%20English/R704Eng.pdf
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