DANGERS OF ‘NUDGE’ POLICIES: Evidence from a behavioural campaign to reduce traffic accidents, which increased the number of crashes

Behavioural interventions (or ‘nudges’) have flourished as a low-cost and easy-to-implement way of encouraging socially desirable actions. Examples include showing people how their electricity usage compares to their neighbours or sending text messages reminding people to pay fines.

Many of these interventions are designed to seize attention at a time when they can make the desired action. Unfortunately, as new research shows, seizing people’s attention can crowd out other important considerations, with potentially costly consequences.

Take the following example: a behavioural campaign with the stated objective of reducing traffic crashes, the leading cause of death of 5 to 45-year olds worldwide. This campaign displays the year-to-date count of roadside fatalities on already available dynamic message signs (for example, ‘1669 deaths this year on Texas roads’).

These fatality messages are designed to be capture attention, with official statements describing them as ‘in your face’ and ‘sobering’, Because of its low cost and ease of implementation, this campaign has spread to at least 27 US states since 2012, affecting at least 90 million drivers. Research by Jonathan Hall and Joshua Madsen shows that, contrary to intent, showing these fatality messages increases the number of crashes.

Using data from Texas, the researchers compared the hourly number of crashes that occur 1-10 kilometres downstream of each digital message sign the week the fatality messages are shown to the hourly number of crashes over those same distances during the other weeks of the same month. 

They find that there are 2-3% more crashes during the weeks the fatality messages are shown. Using statistical techniques to adjust for the effect of weather, holidays and location-specific factors reduces the magnitude of the impact roughly in half.

The hypothesis for why these fatality messages cause more crashes is that they are distracting and make drivers anxious. The evidence for this is that:

  • The number of crashes caused by the message increases along with the displayed number of fatalities. Higher fatality counts are associated with significantly more crashes, whereas lower fatality counts are associated with fewer crashes. 
  • Fatality messages cause the largest increase in crashes in January (which displays the prior year’s total in Texas) and cause marginally fewer crashes in February (when the fatality count resets and is at its lowest).
  • The messages cause the largest increase in crashes in places where the road network is more complicated. 
  • Fatality messages increase the number of multi-vehicle crashes, but not single-vehicle crashes, consistent with them distracting drivers and leading to small mistakes, such as drifting out of their lane, rather than large errors, such as driving off the road.


This research shows that behavioural interventions, designed to be grab people’s attention, can distract them, causing the intervention to backfire with costly consequences. 




Jonathan Hall
Assistant Professor, Department of Economics and Munk School of Global Affairs and Public Policy, University of Toronto

Full research paper: https://papers.ssrn.com/abstract=3633014