Normally a two-stage process is used to try and identify so-called "blackspots". In the first stage a limited number of apparently dangerous locations is selected from all sites on the basis of their accident history. These are then examined in more detail in the second stage of the process. This paper deals with the first stage of the blackspot identification process which is likened to a sieve. A good "sieve" will retain most sites which require detailed examination and allow to pass most sites which need not to be looked at further. Accordingly, a theory of sieve efficiency is formulated in which the number of sites to be inspected, and the expected numbers of "correct positives", "false positives" and "false negatives" serve as measures of performance. This theory is converted into a procedure for a special but common case. This procedure is applied to a population of Ontario highway ramps and to a population of California drivers. In both cases the object of the screening process is to identify deviant units and the efficiency of the sieve is described by the aforementioned measures of performance. For the covering abstract of the seminar see IRRD 273510.
Samenvatting