It causes follow on---sunsets develop into permanent legislation.

Another procedural aspect that could be included is that behavioral policies could be implemented as so-called sunset laws.Footnote107 A sunset clause causes a statute to expire on a legally specified date.Footnote108 Sunset clauses allow the legislator to govern for a specific limited time. Sunset clauses differ from simple ex post evaluations of a policy or legal provision effect because, in order to be renewed, the clause must be explicitly re-discussed and re-approved. Law and economics scholarship has shown that sunset clauses are more particularly introduced in socially normative and often controversial legislation such as, for example, legislation regulating gun control in the US or domestic surveillance.Footnote109 Temporary legislation (including a sunset clause) may be easier to enact also in controversial policy domains because it governs for a shorter period of time.Footnote110 The major advantage is that it is generally held that this type of legislation allows for an ex post evaluation and learning mechanism.Footnote111 If this evaluation shows that the rules were effective, then they can be adapted and converted into permanent laws.Footnote112

Those arguments may equally apply to the case of behavioral policy-making which is, as one can see from the criticism in both economic and legal scholarship, of a controversial nature. Moreover, scholars encourage the implementation of behavioral policies following experimental procedures in order to facilitate their impact evaluation.Footnote113 The advantage of introducing behavioral policies with a sunset clause is that it facilitates the experiment, while at the same time limiting its duration. An experimental implementation coupled with a sunset clause has, on the one hand, the advantage that the impact of the behavioral policy on the outcome of interest can be estimated. On the other hand, this procedure forces the regulator to base behavioral policy-making (and the eventual extension of sunset clauses) on available evidence. Furthermore, to the extent that behavioral policy-making would have negative or unpredicted consequences (as held by McCrudden and King,Footnote114 who referred to “the dark side of nudging”), the advantage of a sunset clause is that these effects would be limited in time.