Study: Posting road death totals on digital highway signs may be deadly
(Rick Egan | Tribune file photo) Highway sign on I-15, May 1, 2020. A new study says that electronic message signs that list numbers of highway fatalities can cause more accidents in some areas where greater driving concentration is required, such as in heavy traffic.
Utah often posts messages on its electronic highway signs that say how many people have died on the state’s roads so far this year or season. They’re intended to improve safety, but a new study says the practice actually increases accidents.
That’s because the message is so stark that it distracts some drivers and increases crashes nearby, according to a study by Jonathan D. Hall, of the University of Toronto, and Joshua Madsen, of the University of Minnesota.
“We hypothesize that by showing a potentially shocking and morbid statistic, fatality messages increase drivers’ cognitive loads, distracting them and crowding out their capacity to drive safely,” the research paper says.
It notes that Utah is among 26 states that post such messages routinely.
“We’re hoping to help improve traffic safety by discouraging the use of these ‘doom and gloom’ messages,” Hall wrote in an email to The Salt Lake Tribune. “We find that the growing practice of displaying fatality numbers on digital highway message signs (a policy attempt to improve traffic safety) is actually leading to an increased number of crashes.”
The study did not find the same problem with other more mundane messages on the digital highway signs — which in Utah may include jokes, travel times to key destinations or warnings about collisions or congestion ahead.
The study focused on Texas because it posts messages about deaths only one week each month, always the week before the monthly meeting of the Texas Transportation Commission. That allows comparing accidents near signs when fatality messages appear to other times and messages.
The researchers found that over several years, crashes increased by just over 2% within 6 miles downstream when the fatality messages appeared.
“Our back-of-the-envelope calculations suggest that fatality messages cause an additional 2,600 crashes and 16 fatalities per year in Texas alone, with a total social cost of $377 million per year,” the study said.
The study found some other interesting details:
• Fatality messages are more harmful when they report a larger number of fatalities.
• More crashes occur when the messages appear in areas where driving requires more concentration, such as congested areas or those with a series of electronic message signs.
• Fatality messages increase the number of multi-vehicle crashes but not single-car crashes. The authors say that is consistent with increased “cognitive load causing driver to make small mistakes, such as driving out of their lane, rather than large errors, such as driving off the road.”
• When “cognitive loads are low or the message is less distracting, fatality messages plausibly help or have no effect” on accidents, it says.
• Drivers are not getting used to the messages over time. “Fatality messages are associated with an increase in crashes every year, except one, between 2013 and 2017,” it said.
The researchers note that other studies about digital highway signs found that messages about speeding, fog or slippery roads are effective at reducing driving speeds — even though their new study finds that fatality messages “can backfire with costly consequences.”
Robert Miles, director of traffic and safety at the Utah Department of Transportation, said his agency will take a close look at the new study but added that the messages seem to have helped in Utah — which operates its messaging somewhat differently from Texas, including giving numbers for a month or season and not an entire year.
“It’s something we’re going to take a look at,” he said about the study. “We want to take a look at all sources of information to try to improve safety.”
But he adds that “the study doesn’t seem to match our experience.”
He notes that Utah started using the messages in 2015, and fatality rates have continued to drop since then.
Miles said the safety messaging scores high in surveys as something that the public notices. “And people have told us anecdotally through our surveys that, ‘Yes, those messages are making a difference in our lives to help change the way we behave.‘ ”