This report examines variations in road injury crash numbers in South Australia by time of year using injury and fatal crash data from 1982-2013. It was found that there was a statistically significant variation in injury crash numbers by month after accounting for different month lengths. January was found to have 11.7% fewer injury crashes per day than an average month and March was found to have 8.6% more. This pattern seems to have been in place over the entire time period examined. Examining crash rates by crash location indicates that rural injury crashes follow a different pattern with more injury crashes in the warmer months and fewer in the colder months. An examination of particular types of days and days of the year revealed very low injury crash rates for the period from 25 December to 5 January, on public holidays and on Sundays. To a lesser extent there were also some indications of lower rates during school holidays. These can all be associated with less travel for work and school and presumably less travel overall leading to less exposure and less injury crashes as a result. This fits with January being the lowest injury crash rate month (with many people on holidays) and March being the highest (very few public holidays and no school holidays) followed by November, May and February (all with minimal school holidays). The limited available exposure measures do suggest that there is less vehicle travel in January consistent with January’s low daily injury crash rate. While there are some indications that March may have a higher exposure, the evidence is not definitive. The increasing number of large public events in March in recent years may be having an underlying effect on the number of injury crashes in March. However, there is no consistent observable evidence for this in the crash numbers so the size of any effect is probably not large. The proportional variation in fatal crash numbers from month to month is very large. Even with 32 years of fatal crash data, no statistically significant variation by month was found. (Author/publisher)
Abstract