A lot of behavioral interventions are expressly designed to be salient, that is, to grab your attention at the time and place where the desired action is made. Many safety campaigns around the world have been using this technique to reduce traffic accidents by displaying “sobering” messages on billboards. The widely held belief is that those messages can motivate drivers to drive more carefully.
A recent analysis by Hall and Madsen (2022) tells a different story. After measuring the effect of a traffic safety intervention in Texas that uses billboards to display fatality messages, the authors found that displaying these messages increases the number of crashes by 4.5% in a 10 km downstream, which is comparable to raising the speed limit by 5-8 km/h. In fact, the larger the number of fatalities reported in the messages, the more harmful they are. This suggests that fatality messages are too salient in this context, leading to cognitive overload at a time when we need less distractions. As for the long-term effect, the results showed no evidence that fatality messages affect driving behavior outside the intervention period.
This paper is another reminder that behavioral interventions are tools and not truths about behavioral change. Truths about behavior is always found in the context, by which the intervention design is largely inspired.
Full paper: https://doi.org/10.1126/science.abm3427