Road crashes and injuries are random events. As a result there may be considerable fluctuations of the weekly or monthly road toll over a period of time. Even when a longer term downward trend exists, such fluctuations are common for weekly or monthly statistics and sometimes for annual statistics. Targets are set and programmes are developed to achieve the targets. Using recent road toll data, control charts have been developed to identify the situation where the variation is outside the expected range. The use of the charts depends upon the construction of upper and lower limits of likely variation, based on patterns of past performance. If the road toll for a defined period, say a week, is higher than the upper limit it indicates that achievement of the target is increasingly unlikely. If it is lower than the lower limit, it suggests that better than expected results are occurring. This paper discusses the application of control charts for the first nine months of the current year - up to the end of' September 1998. (A)
Samenvatting