The effect of public service advertising (PSA) depends on how it is organised (mass media, local, private; see also the question 'How is public service advertising organised?') but also on the manner of approach.
Many mass media campaigns combine information with police enforcement. In the Netherlands this combination has, among other things, led to increased use of seatbelts and child safety devices and increased use of bike lights  . Likewise, the Goochem-campaign (about seatbelt use) and the Bob-campaign (about drink-driving) have been successful in changing attitudes and behaviour in a positive way . Both campaigns have been qualified as 'best practice' in the SUPREME-manual and are used in a large number of European countries . Also in other countries, such as Australia, New Zealand and the United States, the combination of police enforcement and information has been found to result in improved road safety .
International reviews conclude that PSA has a positive effect on road safety  . However, as most PSA is combined with other activities (such as increased enforcement), there is little evidence for a stand-alone effect of mass media road safety information. A Dutch study  showed that a national PSA campaign on speed had no effect on measured speeds or offences. Places where the campaign was supported by special signs showed a small effect on the driven speeds, but this effect had disappeared a week after the signs were placed. Because of this minimal effect of isolated mass media? campaigns, most information activities in the Netherlands are supported by enforcement. This makes it very hard to determine whether the success of a campaign is the result of information, of enforcement, or of the combination of the two . The little research that has tried to distinguish the effects concluded that the mass media information did not or barely contribute to improved traffic behaviour . This does not mean that been information campaigns can be omitted. Information can indeed contribute to more knowledge and attitude change. It can also contribute to better acceptance of unpopular, but effective measures, such as enforcement.
TeamAlert, the foundation that provides traffic information for young people, mainly uses the local and personal approach. The target group is approached directly and in some projects the target group is approached individually. Various effect studies show that this approach is partially effective, particularly when it comes to increasing knowledge and behavioural intention (see for example effect measurements of the programmes ‘Kruispunt’  and ‘Streetbeat’ ). However, change must be possible: for example, the evaluation of ‘Witte Waas’ (in which information about drugs and alcohol in traffic is given) indicated that the level of knowledge was already pretty high .
Manner of approach
The effect of public service advertising also depends on the approach. Informative, instrumental information can be effective in increasing knowledge, if the level of knowledge prior to the campaign is insufficient. Research by Goldenbeld  found that a campaign for the correct adjustment of the headrest in the car led to an improvement of the observed behaviour: before the campaign 40% had the headrest correctly adjusted; after the campaign, this was 60%.
As yet not much is known about the effects of information that specifically focuses on the social norm. However, there is research that shows that the social norm is important in demonstrating safe traffic behaviour. Young drivers, for instance, were more inclined to make a phone call while driving if they thought their friends supported this . Drivers were also found to be guided more by other traffic in their speed choice than by the speed limit .
Evaluation studies of fear appeals find both positive and negative effects. Generally these effects only refer to changes in behaviour and behavioural intentions. The varied results make it difficult to determine whether fear appeals do indeed result in fewer crashes. Some campaigns were found to be effective, others were not.
+ Research from Australia and New Zealand shows that fear appeal media spots may have a positive effect: a reduction of unsafe traffic behaviour. According to the Australian research the number of road crash casualties declined by 5 to 7% as a result of the media spots  .
0 There are also road safety studies which found that fear appeals have no effect. A meta-analysis of 13 studies  for example, found no effect.
- Fear appeals having the opposite, negative effect, however, is also possible. This was the case with information campaigns on drink-driving , speed behaviour  , binge drinking  and on distraction in traffic . A Dutch study found that the male subjects found speeding less dangerous after seeing a television spot. They were less willing to keep to the speed limit and downplayed the message ('speeding is dangerous') and the behavioural recommendation ('don’t drive fast, keep to the limit') . Various Belgian studies indicate that although fear appeals have a short-lived effect on attitudes and opinions, the public quickly gets used to the element 'fear'. This would cause the effects to diminish more rapidly than the effects of information based on positive emotions .