The effectiveness of speed control and accompanying publicity in Friesland; Effects on speeding offences and crashes on 80 km/h and 100 km/h roads during the 1998-2002 period In the Province of Friesland in February 1998, an ambitious traffic control project was started to improve road safety in the province. In this project, the traffic control on driving speeds on the most dangerous 80 and 100 km/h rural roads was intensified. In addition, extra efforts were made throughout the whole province to lessen drunk driving, red light running, and not wearing a seatbelt or crash helmet. This evaluation study was limited to speed control and studies the effects on speeding offences and crashes with motor vehicles of the intensified control and the accompanying publicity. This is a sequence to a previous evaluation. The present evaluation used crash and driving speed data during a longer period, together with better analysis methods. With regard to speeding offences, the analyses show a clear difference between those road segments along which extra control was carried out and the reference road segments where this did not happen. On the 80 km/h roads, the percentage of offenders on segments with intensified control dropped from more than 30% in 1997 to 15% in 2001. On those segments without control, however, this remained above 25% during the same period. The greatest reduction in speeding offenders occurred on roads closed to non-motor vehicles. On the 100 km/h road segments with extra control, there was a significant reduction in speeding offences, from about 15% in 1997 to about 8% in 2001. During the same period, the reduction on 100 km/h road sections without extra control, was not significant: from 16% to about 13%. The effect of the intensified speed control was also quite positive on the numbers of injury crashes (all severities) and severely injured casualties (deaths and in-patients). The estimates have to be treated with care because the confidence margins around the effects found are very large. This is mainly due to the small numbers of crashes and casualties. The most important results were: - On road segments with extra control there is an average saving of 21% (5% - 34%) in the number of crashes with motor vehicles, compared with the other rural roads in Friesland. - On road segments with extra control there is an average saving (also) of 21% (1% - 37%) in the number of severely injured casualties of crashes with motor vehicles, compared with the other rural roads in Friesland. - It is possible that a small part of this effect can be attributed to the phenomenon of 'regression to the mean', but this will only be several percentage points. Regression to the mean can be the result of the fact that road segments with the most crashes were selected for extra control. Roads that, by accident, had a greater than average number of crashes in the selection period, will probably have had less crashes during the following period; this is just because of the random fluctuations (i.e. even if no measures at all had been taken). Seeing as 5-year crash data were used to select road segments for extra control, the effect of random fluctuations will probably be small, and with it, the contribution of this phenomenon to the safety effect. - Whether, and to what extent, other factors have contributed to the positive development on the road segments with extra control cannot be exactly determined. There are, however, clear indications that the safety effect started immediately after 1998. This could not be expected if it was the consequence of (mainly gradual) changes in, for example, traffic volume and traffic measures. The question of whether the implementation or the effects of this project have been optimal is difficult to answer because only one implementation type has been tried out and evaluated. In spite of this, from the successful characteristics and elements of this project, we can make a number of recommendations: - Intensified control must be aimed at structurally dangerous road segments. This increases the credibility of the extra control. The choice of road segments should, therefore, be based on a longer period of crash data, preferably four or five years. - 4000-5000 control hours a year are sufficient to lower the percentage of offenders along a road segment of about 120 kilometres. - Intensive publicity campaigns increase the subjective chance of being caught. This is one of the central mechanisms of effective control. - Variation in time and place of the control activities and variation of the control method contribute to the unpredictability of controls. In the literature, these are often regarded as a precondition for success in traffic control. Finally, the following three matters are anyway important for the future. Firstly, it is important to estimate more exactly what the effects are of control during a period of a number of years. This is already possible by analysing the data of a one or two year longer control period. Secondly, it is important to establish the extent to which the effects found in Friesland can also be achieved in other regions. This requires further study, in which the present research method should be applied to roads in a number of other provinces. Thirdly, in this study it was only possible to determine quantitative relations between the type and intensity of control and its effects to a very limited extent. A possibility of getting to know more about such matters is a) a similar study in a larger area, b) systematically monitoring the exact road and traffic characteristics, and c) varying the control activities.