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Abstract
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Although behavioral interventions are designed to seize attention, little consideration has been given to the costs of doing so. We estimated these costs in the context of a safety campaign that, to encourage safe driving, displays traffic fatality counts on highway dynamic message signs for 1 week each month. We found that crashes increase statewide during campaign weeks, which is inconsistent with any benefits. Furthermore, these effects do not persist beyond campaign weeks. Our results show that behavioral interventions, particularly negatively framed ones, can be too salient, crowding out more important considerations and causing interventions to backfire-with costly consequences.
INTRODUCTION
Policy-makers are increasingly turning to behavioral interventions such as nudges and informational campaigns to address a variety of issues. Guidebooks say that these interventions should "seize people's attention" at a time when they can take the desired action, but little consideration has been given to the costs of seizing one's attention and to the possibility that these interventions may crowd out other, more important, considerations. We estimated these costs in the context of a widespread, seemingly innocuous behavioral campaign with the stated objective of reducing traffic crashes. This campaign displays the year-to-date number of statewide roadside fatalities (fatality messages) on previously installed highway dynamic message signs (DMSs) and has been implemented in 28 US states.
RATIONALE
We estimated the impact of displaying fatality messages using data from Texas. Texas provides an ideal setting because the Texas Department of Transportation (TxDOT) decided to show fatality messages starting in August 2012 for 1 week each month: the week before TxDOT's monthly board meeting (campaign weeks). This allows us to measure the impact of the intervention, holding fixed the road segment, year, month, day of week, and time of day. We used data on 880 DMSs and all crashes occurring in Texas between 1 January 2010 and 31 December 2017 to investigate the effects of this safety campaign. We estimated how the intervention affects crashes near DMSs as well as statewide. As placebo tests, we estimated whether the chosen weeks inherently differ using data from before TxDOT started displaying fatality messages and data from upstream of DMSs.
RESULTS
Contrary to policy-makers' expectations, we found that displaying fatality messages increases the number of traffic crashes. Campaign weeks realize a 1.52% increase in crashes within 5 km of DMSs, slightly diminishing to a 1.35% increase over the 10 km after DMSs. We used instrumental variables to recover the effect of displaying a fatality message and document a significant 4.5% increase in the number of crashes over 10 km. The effect of displaying fatality messages is comparable to raising the speed limit by 3 to 5 miles per hour or reducing the number of highway troopers by 6 to 14%. We also found that the total number of statewide on-highway crashes is higher during campaign weeks. The social costs of these fatality messages are large: Back-of-the-envelope calculations suggest that this campaign causes an additional 2600 crashes and 16 fatalities per year in Texas alone, with a social cost of $377 million per year.
Our proposed explanation for this surprising finding is that these "in-your-face," "sobering," negatively framed messages seize too much attention (i.e., are too salient), interfering with drivers' ability to respond to changes in traffic conditions. Supporting this explanation, we found that displaying a higher fatality count (i.e., a plausibly more attention-grabbing statistic) causes more crashes than displaying a small one, that fatality messages are more harmful when displayed on more complex road segments, that fatality messages increase multi-vehicle crashes (but not single-vehicle crashes), and that the impact is largest close to DMSs and decreases over longer distances. We discuss seven alternative hypotheses, including the possibilities that treated weeks are inherently more dangerous and that fatality messages help in the long run. We provide evidence inconsistent with each alternative hypothesis.
CONCLUSION
Our study highlights five key lessons. First, and most directly, fatality message campaigns increase the number of crashes, so ceasing these campaigns is a low-cost way to improve traffic safety. Second, behavioral interventions can be too salient, crowding out more essential considerations and causing the intervention to backfire with costly consequences. Thus the message, delivery, and timing of behavioral interventions should be carefully designed so they are not too salient relative to individuals' cognitive loads when the intervention occurs. Third, individuals don't necessarily habituate to behavioral interventions, even after years of treatment. Fourth, the effects of interventions do not necessarily persist after treatment stops. Finally, it is important to measure an intervention's effect, even for simple interventions, because good intentions do not necessarily imply good outcomes.
Language: en |