Benjamin Franklin once said there are two certainties in life: death and taxes. Now, researchers have found that taxes might make death just a little more certain.

Deaths from traffic accidents rise 6% on tax day, that mid-April paroxysm of collective financial agony, according to a study published in Wednesday’s edition of the Journal of the American Medical Assn.

A pair of Canadian researchers tallied up U.S. tax day traffic fatalities for each year between 1980 and 2009, then compared the figures to those from two “control” days, exactly one week before and one week after. On average, they found, there were 226 deaths on tax day — 13 more than on non-tax days.

The rise in e-filing — which would presumably keep procrastinators from speeding recklessly to the nearest post office — doesn’t appear to have put a dent in the trend, said Dr. Donald Redelmeier of the University of Toronto’s Institute of Health Policy, Management and Evaluation, who led the study.

Perhaps that’s because the heightened danger involves more than a deadline dash to a mailbox. Stress is a likely culprit, Redelmeier said: In general, most accidents are the result of human error, not mechanical failure, and stress has been shown to significantly worsen performance behind the wheel.

About 20% to 25% of American taxpayers file their returns within the last two weeks before the deadline, according to the Internal Revenue Service.

But even for those who don’t procrastinate, the arrival of tax day can prompt enough distraction to spell trouble, said William Helton, a psychologist at the University of Canterbury in Christchurch, New Zealand, who was not involved in the study.

“It might not even be that you’re anxious,” Helton said, but “you’re thinking about the nitty-gritty: ‘Line 27, did I put the right number in?’ ”

And then there are all those other edgy drivers to worry about, Redelmeier said, pointing out that his study used data from the National Highway Traffic Safety Administration but did not determine the circumstances behind those deadly accidents or ascertain who was at fault.

“Just because you’ve filed early doesn’t mean this is not going to affect you,” he said. “If you’re on the road for 20 to 25 minutes, it brings you into contact with 100 other drivers, any one of which could change your life forever.”

More research is needed to untangle the link between tax day and traffic deaths, said Dr. Ricardo Martinez, who headed the traffic safety administration in the 1990s. Among the outstanding questions: Does the increased risk come from a small number of really stressed-out drivers — last-minute filers, perhaps — or a large number of slightly edgy ones?

Either way, the researchers emphasized that stress is the issue in question here, not Uncle Sam. “We are not advocating an abolition of taxes,” Redelmeier said. “That does not make the problem go away.”

amina.khan@latimes.com