Safe and credible speed limits
To invoke road users to keep to the speed limits, it is essential that these limits are safe and credible. A credible limit means that it is considered logical by the road user, i.e. the limit corresponds to the expectations that a road's layout and traffic environment evoke. Whereas the idea may not be new and many countries have such a requirement in their speed limit regulations, there seems to be substantial room for improvement.
Correspondence between speed limits and road layout can be realised by fitting the layout to the limit or the limit to the layout. On some roads the limit may need to be raised, whereas on others it may need to be lowered. Another important consequence of the concept of credible limits is that at a place where one limit changes to another one, as for example is the case when leaving an urban area, road users should always be able to see a clear change in road layout. The ERSO text on Speeding gives further details about credible speed limits.