Traffic accident statistics on signs may actually cause more crashes

Matthew Sparkes is a writer.

There is compelling evidence that electronic signs that highlight traffic deaths cause accidents.

Although the messages are displayed in many US states, Jonathan Hall at the University of Toronto in Canada and his colleagues chose to examine crash data from Texas because the state uses electronic signs for fatality warnings just one week out of each month.

The researchers compared the number of crashes between the two years before and after the signs were put up. The number of crashes on the 10 kilometres of road after the sign was displayed increased by 4.5 per cent. There were more crashes and deaths caused by fatality messages in Texas.

The effect is down to distraction and the increase in the driver's cognitive load. I want to make it clear that we don't have that. I think we have compelling evidence.

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The number of deaths displayed on a sign changes its impact as larger numbers are more shocking. The team saw a big drop in crashes in February compared to January, because the state fatality numbers were reset each year in February.

Hall says his team has written to all states that show warning messages and asked them to collaborate on further research, but they have received little positive response. He says that they haven't done that because there is a presumption that the signs can hurt.

The Texas Department of Transportation didn't respond to a request for comment, but is understood to no longer display such warning messages above highways.

There is a journal reference called Science.