‘Nudging’ drivers to death: Highway death toll messages cause more crashes

By: Munk School of Global Affairs & Public Policy with files from the University of Minnesota’s Carlson School of Management

^{Jonathan Hall}

April 21, 2022

Electronic highway messages are one of the ways that policymakers have been using to raise awareness of roadway dangers. These ‘nudges’ are meant to “seize people’s attention” at a time when they can take action but data suggests they may have the opposite effect.

A new study in Science by University of Toronto assistant professor Jonathan D. Hall and University of Minnesota assistant professor Joshua Madsen evaluated the effect of displaying crash death totals on highway message boards (e.g., “1669 deaths this year on Texas roads”). They found that these displays — used in at least 28 U.S. states — actually lead to more crashes.

Hall and Madsen’s study focuses on Texas, where officials chose to display these messages for one week of each month. The researchers compared crash data from before the campaign (Jan. 2010 – July 2012) to after it started (Aug. 2012 – Dec. 2017) and compared the weekly differences within each month during the campaign. Their results showed the following:

There were more crashes during the week with fatality messaging compared to weeks without.
Displaying a fatality message increased the number of crashes over the 10 km (6.21 mi) following the message boards by 4.5%. This increase is comparable to raising the speed limit 3-5 mph or reducing highway troopers by 6-14%, according to previous research.
Their findings suggest fatality messages cause an additional 2,600 crashes and 16 deaths per year in Texas, with an estimated social cost of $377 million each year.
The researchers suggest this “in-your-face” messaging approach weighs down drivers’ “cognitive loads,” temporarily affecting their ability to respond to changes in traffic conditions.

“The messages increased the number of multi-vehicle crashes, but not single-vehicle crashes,” said Hall, an assistant professor in U of T’s Department of Economics and the Munk School of Global Affairs & Public Policy. “This is in line with drivers with increased cognitive loads making smaller errors due to distraction, like drifting out of a lane, rather than driving off the road.”

The researchers found the bigger the number in the fatality message, the more harmful the effects. The number of additional crashes each month increased as the number of roadway deaths rose throughout the year, with the most additional crashes occurring in January when the message stated the annual total. They also found that crashes increased in areas where drivers experienced higher cognitive loads, such as heavy traffic or driving past multiple message boards.

“Driving on a busy highway [and] having to navigate lane changes is more cognitively demanding than driving down a straight stretch of empty highway,” said Madsen, who teaches at U of T’s Carlson School of Management. “People have limited attention. When a driver’s cognitive load is already maxed out, adding on an attention-grabbing, sobering reminder of highway deaths [can] become a dangerous distraction.”

However, the researchers found there was a reduction in crashes when the displayed number of deaths were low and when the message appeared where the highways were less complex. Madsen says this suggests that at times the messaging was not as taxing on drivers’ attention.

While the use of highway fatality messaging varies by state, the researchers suggest that agencies should consider alternative ways to raise awareness.

“One of the key takeaways from this research was that fatality message campaigns increase the number of crashes, so stopping these campaigns is a low-cost way to improve traffic safety,” says Hall. “This study illustrates why it is so important to study the effects of ‘nudges’ and other behavioural interventions. Just because a policy is well-intentioned doesn’t mean that it will result in a good outcome.”

This research was supported by the Social Sciences and Humanities Research Council of Canada and the European Union’s Horizon 2020 research and innovation programme.

Follow this research in the news:

Texas reminded motorists to drive safely. It didn’t work out as planned. (LA Times)
Highway Death Toll Messages Linked to Rise in Car Crashes, Study Says (Wall Street Journal)
Highway Death Toll Warning Signs May Cause More Crashes, Not Less (USA News)
The downside of displaying road fatality numbers (The Hill)
Traffic accident statistics on signs may actually cause more crashes (NewScientist)
Highway signs showing traffic deaths don’t reduce crashes (Science)
Highway death toll signs associated with more crashes, researchers find (U of T News)