Physical speed reduction measures considerably affect driving speed at locations where the measure applies. Dynamic lane control signs with dynamic limits contribute to more homogeneous speeds, fewer intensive braking manoeuvres and fewer crashes and near miss crashes. The effects of softer measures, such as rehabilitation courses, publicity campaigns, community projects and nudging are minor and short-term.
Physical speed reduction measures
Physical speed reduction measures make driving at a (too) high speed physically impossible and are therefore very effective in reducing speed, at any rate near the location of the measure.
Physical speed reduction measures primarily imply speed humps, road narrowing, and axis offsets. A roundabout will automatically ensure a lower speed and may therefore also be considered a physical speed reduction measure. To achieve a maximum effect, the physical speed reduction measures should be implemented at the appropriate location, with appropriate spacing and dimensioning. Speed humps that are too low or too far apart will have little effect on speed. A speed hump at a location where speed is not a problem, will not benefit acceptance of this kind of measure. Dutch guidelines for applying physical speed reduction measures [29] [41] are published by CROW, technology platform for transport, infrastructure and public space.
Speed limits on dynamic lane control signs
Speed limits on dynamic lane control signs lead to more homogeneous speeds, a reduction of the number of crashes and near miss crashes [42] and to fewer intensive braking manoeuvres [43]. Dynamic lane control signs allow for limit reductions should weather and traffic conditions so require and, therefore, have an important signalling effect in case of incidents and deviating conditions. Thus, dynamic lane control signs effectively complement general speed limits and time-varying limits. Dynamic lane control signs should not be used to display the general limit, because this would be detrimental to the aforementioned signalling effect [44] [45].
Speed limits and other relevant information on dynamic lane control signs have mostly been implemented at motorways. The limits they indicate are not advisory speeds, as is sometimes supposed, but legal maximum speeds. If the speed limit on the dynamic signs is different from the general limit or the road sign limit, the lowest speed is mandatory. Dynamic lane control signs mean to draw the driver’s attention to special conditions that require a lower speed; in particular, in case of congestion or incidents upstream, but also in bad weather conditions, such as slipperiness or fog. Factors affecting compliance with the dynamic speed limits are, among other things, the approach speed and the spacing of consecutive dynamic lane control signs [46].
Educational measures or rehabilitation courses
In the Netherlands, people having committed one or two serious offences (other than alcohol related offences) can be obliged to participate in a rehabilitation course called ‘Educational Measure Behaviour and Traffic’ (EMBT). However, this rehabilitation course, proves to have little effect on road user behaviour.
In case of serious offences, the Central Office for Motor Vehicle Driver Testing (CBR) may impose a rehabilitation course or ‘educational measure’ as an administrative penalty. The Dutch EMBT is specifically meant for drivers who have repeatedly displayed undesirable driving behaviour during a single car journey, but the measure may also be imposed for a single very serious speeding offence. An evaluation showed that 30% of the drivers who had completed an EMBT in 2013 became involved with the judicial authorities once again; 20% committed another traffic offence within two years, and 12% were charged with an EMBT related offence within two years [47]. More information about can be found in SWOV fact sheet Traffic enforcement.
Influencing behaviour by publicity campaigns, community projects and nudging
The aforementioned speeding measures may be considered as hard behavioural measures. Softer behavioural measures are aimed at providing general or more targeted information (publicity campaigns and several community projects) that entice the public (nudging). As far as the measures have been evaluated, they appear to have limited time and place effects.
Publicity campaigns
There is little evidence for the effectiveness of publicity campaigns on road safety by making use of mass media only (see SWOV fact sheet Public service advertising). A more personal and local form of publicity is often more effective [48]. This was confirmed by an evaluation of the effect of the Dutch campaign Respect the speed limit [30].
on speeding behaviour in the urban area: in general, no effect was found on driving speed and the number of speeding offences. In areas where the general campaign was supported by motto billboards along the road, a small, albeit temporary, effect on driving speed was found.
Community projects
Particularly in 30km/h areas, community projects may lead to a small, statistically insignificant reduction of driving speed, while they do not have a measurable effect on feelings of unsafety. This was shown by an evaluation of several community projects aimed at speeding by Bax and colleagues [49]. The previous evaluations they described did not show any convincing effects of community projects either. Veilig Verkeer Nederland (Safe Traffic Netherlands) organises and supports community projects to create and increase awareness (of one’s own) behaviour, including speeding behaviour. Examples are a bin sticker campaign, braking distance demonstrations and having people design road signs.
Nudging
Nudging, or automatic influencing of individual behaviour, implies tempting people to display desired behaviour without coercion. Nudging can affect behaviour, but only slightly, and it may not be easy to generalise the possible effects, nor to make them last [50]. Without additional measures, nudging does not appear suitable for realising lasting behavioural changes. An actual application aimed at drivers’ speeding behaviour confirms this general finding. Placing Dick Bruna drawings – that are associated with children – on billboards along 30km/h roads resulted in a reduction of average speed (of 0,75 km/h), of the V85 (of 1,5 km/h), and of the share of offenders (of 5%), a minor effect that, moreover, disappeared within a few weeks [51]. In the European Project MeBeSafe, different forms of nudging were developed and tested in practice. The field study results showed mostly positive effects, but long-term effects were not studied [52].
