Do Electronic Signs Displaying Number of Traffic Fatalities Actually Cause More Crashes?

From Jonathan Hall & Joshua Madsen, Are behavioral interventions too important? Traffic safety messages provide evidenceIn the journal Science:

Policy-makers are increasingly turning to behavioral interventions such as nudges and informational campaigns …. According to Guidebooks, these interventions must “seize the attention of people” when they are able to take desired action. But little has been done to consider the cost and possibility that the interventions could overshadow other important considerations.

We estimated these costs in the context of a … 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….

Utilizing data from Texas, we estimated the effect of showing fatality messages. Texas offers a perfect setting as the Texas Department of Transportation decided to display fatality messages beginning in August 2012, for one week per month. This week was before the TxDOT monthly board meeting. We can measure the effect of intervention by holding the road segment fixed, year, month and day of the week. To investigate the impact of this safety campaign, we used 880 DMSs as well as all Texas crashes between January 2010 and December 2017. The intervention has an impact on crashes in the vicinity of DMSs and 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….

We found, contrary to expectations of policy makers, that traffic accidents are actually more likely when fatality messages are displayed.

Campaign weeks show a 1.52% increase of crashes within five kilometers of DMSs. The increase slightly decreases to 1.35% over the 10km following DMSs. {Because of imperfect compliance and competing demands, traffic engineers do not display fatality messages on all DMS hours during campaign weeks, implying that the effect of displaying a fatality message on a DMS is even larger.} The effect of showing a fatality warning message on DMS hours was determined using instrumental variables. We found an increase of 4.5% in accidents 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%…. Based on back-of the-envelope calculations, it is estimated that 16 more fatalities are caused by this campaign in Texas each year. The social cost to Texas of this campaign would be $377 million.

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….

For the tip, thanks to Prof. Glenn Reynolds from InstaPundit