Background: As far as the author is aware no statistics of traffic accidents were so far concerned with the problem of a possible correlation of their frequency with the position of the moon, i.e. the lunar phase. Sudden cardiovascular deaths and some meteorological parameters (mean precipitation, atmospheric pressure and temperature) have this correlation and in most instances it is highly significant.
Methods and results: The authors processed data pertaining to a total of 60,142 traffic accidents in the former South Moravian region in 1983, 1984, 1990, 1991 and 1992. The number of accidents on every particular day was classified according to the lunar phase. It was revealed that the frequency of accidents increases twice in the course of the lunar cycle (i.e. in the semilunar stages). The first increase is on the second and third day following new moon (t = 1.89 < 1.96 which is closely beneath the 5% level of statistical significance, p > 0.05). The second increase is more prolonged and more marked and starts already on the first day before full moon and persists after full moon with a maximum on the second day after full moon (t = 1.32 < 1.96, which again is beneath the 5% level of statistical significance, p > 0.05). The curve of the frequency of traffic accidents follows practically the same course as the curve of changes of atmospheric precipitation except for the day before full moon and the day after full moon.
Conclusions: The revealed semilunar increase of traffic accidents is probably associated with the bi-phasic change of atmospheric precipitations with their increase closely after new moon and after full moon. However, one day before full moon the atmospheric precipitation is low and the increase in the accident rate on these days might be explained by the effect on the human factor, i.e. psychosomatic changes during the period near the full moon.