Common Tread

Does the full moon cause motorcycle crashes?

Dec 14, 2017

We know about the usual motorcycle crash hazards, from distracted drivers to drinking and riding to target fixation. But can the full moon make you crash?

That’s the finding of an academic study of nighttime fatal motorcycle crashes over the past 40 years that compared full-moon nights to other control nights. The researchers came to the supposition that the tendency to be distracted by the sight of a full moon leads to a small but significant increase in fatal crashes.

The study was done by Donald A. Redelmeier, a professor of medicine at the University of Toronto, and ldar Shafir, professor of psychology and public affairs at Princeton, University. It used data from the U.S. National Highway Transportation Safety Administration’s Fatality Analysis Reporting System, which tracks fatalities on the public roads. The researchers included every full moon from 1975 through 2014, 494 in all. They looked at the number of fatal crashes from 4 p.m. to midnight and from midnight to 8 a.m. and also compiled the number of fatal crashes on nights a week earlier and a week later to create 988 control nights for purposes of comparison.

The results: There were 13,029 fatalities on the nights studied and that broke down as 9.1 deaths per full-moon night compared to 8.64 per control night. In other words, we could expect one more person to die in a nighttime motorcycle crash for every two nights with a full moon.

The researchers also looked at the 65 so-called “supermoon” nights during the study period. A supermoon is when the moon is both full and at its closest distance to earth in its orbit, which makes it up to 30 percent brighter. There were 10.82 fatal crashes per supermoon night.

The researchers repeated their study using data from Canada, the U.K., and Australia, but those studies were not considered statistically significant, because the data did not go back as far. The findings in those other countries were consistent with the findings based on the U.S. data, however.

When the crashes were broken down by the rider’s age, gender or helmet use or by the size or age of the motorcycle, the results did not change. Nights with a full moon still showed more fatalities.

The conclusion the researchers come to is that the moon occasionally distracts a motorcycle rider, causing a crash that’s fatal.

“The relative effect size associated with the full moon is small and only important because of the large number of people repeatedly exposed,” the study states.

“Several aspects of attention and perception could explain an association between the full moon and motorcycle fatalities. A full moon is infrequent and spectacular, thereby creating a natural distraction. The full moon is large and bright against a dark sky, and thus provides a striking contrast of luminance. It can appear abruptly to a motorcyclist, such as when riding around buildings, through turns, past trees, and over hills. A full moon also creates optical illusions that engender wonderment and tends to rise above the horizon in the night hours exactly at the time motorcycle crashes generally predominate. Beyond these, a full moon might contribute to increased outdoor activity of all types, including more frequent travel, faster speeds, longer distances, unfamiliar routes, added cross traffic, and mixtures of less experienced travelers.”

So now riders have another new excuse for those times it goes sideways, assuming you live to tell about it. “I had to lay ‘er down because I was stunned by the full moon.”