Performance, outcome and output measures

Police organizations have their own administrative recording system for policing activities. These days, increasing pressure is put upon police managers to justify the use of policing resources. Ideally, the monitoring system of policing activities provides data and arguments for this. For traffic enforcement and speed enforcement, a monitoring system should be aimed at showing relationships between policing resources (performance), effects on traffic behaviour, speed, (outcome) and, ultimately, effects on road safety (outcome). We can distinguish between performance measures and outcome measures [60]. Performance measures define what the police actually do on the streets, i.e.: how often, for how long and on which locations do they check speeding behaviour? Outcome measures should reflect the effects of enforcement on behaviour and on the consequences of behaviour, in the case of traffic enforcement, such as traffic crashes.

A further distinction can be made between outcome and output measures (Footnote; Swadley & McInerney do not make this distinction and list a number of infringements as an outcome measure). Outcome measures refer to intended outcomes, i.e. safer behaviour. ‘Output’ measures refer to administrative outcomes generated by policing activities such as for instance the number of tickets or the number of court cases that are a result of policing activities, but are not the main aim of these activities. Goldenbeld [27] argues that output measures such as the number of speed fines cannot be seen as a good indicator of the effectiveness or quality of police enforcement. Although there may be good administrative reasons to keep track of these data, the data is not very informative as to the quality of speed enforcement. Tables 2 and 3 provide the performance measures for speed cameras and non-camera operations as proposed by Swadley and McInerney [60].

Table 2 Speed camera performance measures (Source: Swadley & Mclnerney, 1999)

Table 3 Non-speed camera performance measures (Source: Swadley & Mclnerney, 1999)

The most direct form of outcome measurement is speed itself. Data from speed cameras is of limited use to evaluate effects on speed behaviour since it can be assumed that drivers will become familiar with camera sites and will alter their normal speed behaviour. Covert speed monitoring which is not connected with enforcement activities is necessary to obtain true and valid data on speed behaviour when enforcement activities are not present.

The SafetyNet report Safety Performance Indicators: Theory provides further detail on the method to set up reliable speed measurement.