How safe was 2004?; Analysis of the decrease in number of road deaths in 2004. In 2004 there was a sharp decrease in the number of road deaths compared with 2003. This reduction of 19% is spectacular: the number fell from 1088 in 2003 to 881 in 2004. This is the largest reduction ever in the Netherlands. Three questions need to be answered. Is the data correct? What was the role of coincidence? What really happened? SWOV investigated these three aspects, and the results were as follows: 1. The data is correct. They are just as reliable as in other years. Nothing was found to indicate that a lower registration rate caused the numerical reduction. 2. Coincidence can have played an important role in the difference between 2003 and 2004. A simple trend analysis shows that, with reasonable assumptions about the role of coincidence, the difference of 207 deaths consists of five components (the numbers in brackets give an indication of the size of the component): - there was a random peak in 2003 (48), - explicable circumstances made 2003 less safe (16), - a decreasing trend (29), - there was a random drop in 2004 (48), and - explicable circumstances made 2004 safer (66). These 66 deaths account for 6.6% of the trend. These figures are very uncertain because the coincidence factor cannot be calculated exactly. To do this, a model that sufficiently accurately predicts the expected number of road deaths is necessary. In comparison with the trend, the peak in 2004 is not larger than the exceptions in previous years. In other words, 2004 is less exceptional than the difference with 2003 implies. 3. No explanatory influence factors were found to explain the decrease in 2004. Explanations were either too small, unresearchable, or too speculative. For example, the effect of extra enforcement possibly contributed considerably to the decreasing trend, but is insufficient to explain 2004. In general, meteorological effects have been empirically studied, but are not convincing enough to explain the decrease in 2004. What remains is that the growth in kilometres travelled seems to have stagnated: the numbers of delivery vans has stabilized and the numbers of kilometres travelled in lease cars has declined. This could explain a decrease of 6.6% road deaths, but it is speculative. This subject is an interesting starting point for a study by the Road Safety Planning department of SWOV.
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