PRINCETON, N.J.--Distracted drivers, like those who text behind the wheel, are a danger to themselves and to others. Even a brief, momentary glance away from the road can result in life-threatening consequences.
Research published Dec. 11 in The BMJ points toward another potential distraction for motorists: the full moon, gracing the sky with its brightness around 12 times a year, and the dazzling supermoon, which comes into focus around once a year.
The researchers found that on nights illuminated by a full moon, fatal motorcycle accidents increased by 5 percent compared to nights without a full moon. On evenings when the supermoon decorated the sky, this increased to 32 percent. The study included data from the United States, the United Kingdom, Canada, and Australia.
While this observational data cannot prove any firm conclusions, the researchers warn drivers of the risks of seemingly minor distractions, urging constant attention while driving at all times.
"Drivers face a number of distractions behind the wheel -- from texting, to phone calls to road obstructions and more," said study co-author Eldar Shafir, the Class of 1987 Professor in Behavioral Science and Public Policy and professor of psychology and public affairs at the Woodrow Wilson School of Public and International Affairs. "Our study adds to the literature that small distractions can sometimes lead to life-altering consequences."
"Glancing at the full moon takes the motorcyclist's gaze off the road, which could result in a loss of control," said the study's lead author Redelmeier, professor in the Department of Medicine at the University of Toronto. "The average ride on a motorcycle is more dangerous than a drunk driver with no seatbelt traveling the same distance. Because of this, we recommend riders and drivers orient their attention, ignore distractions, and continuously monitor their dynamic surroundings."
Redelmeier and Shafir hypothesized that people's attention may be naturally drawn to a full moon, thereby potentially contributing to fatal motorcycle crashes. To test this, they analyzed data from the official United States registry of motor vehicle crashes from 1975 to 2014, during which time 494 full moons and 65 supermoons appeared. They calculated the number of fatal crashes on full moon nights compared to nights with a quarter moon (one week before and after the full moon).
The researchers defined a full moon as the one night each month when the entire facing surface of the moon was illuminated. They also included the rare occasions in which two full moons appeared in the same month. They studied a 16-hour time frame, which they labeled as nighttime motorcycle activity, which fell between 4 p.m. and 8 a.m. The overall study duration spanned 40 consecutive years.
They found 4,994 fatal crashes occurred on the nights with a full moon, which is equal to 9.10 crashes per night. In contrast, a total of 8.64 fatal crashes per night occurred on nights without a full moon. Fatalities increased further under a supermoon, amounting to a total of 703 fatal crashes, or 10.82 fatal crashes per night. This means that for every two full moon nights, there was one additional fatal crash. Under the supermoon, this increased to two additional deaths.
Overall, there was a total increase of 226 additional fatal crashes on nights with a full moon during the entire study period.
"While these figures might seem low on the surface, they are quite significant," Redelmeier said. "All of these deaths could have been prevented completely by small difference in behavior."
The typical motorcyclist was a middle-aged man riding a street bike with a large engine in a rural location, who experienced a head-on front impact. Less than half were wearing a helmet. Seventy-three percent of the crashes occurred during the hours before midnight, and 27 percent occurred during the hours after midnight.
The researchers repeated their analyses in the United Kingdom, Canada and Australia and found similar results.
The researchers highlight the limitations of the study. For example, other distractions and traffic hazards were not taken into account, and neither were factors including the prevailing weather or moon visibility. And while they used large datasets, like any routinely collected data, errors could have been made when the data was entered.
Nevertheless, the study's findings highlight the importance of safe, careful and attentive driving, under all conditions.
"We encourage motorcycle riders to wear a helmet, activate headlights, scan the road surface and be wary of other vehicles," Redelmeier said. "The best approach to safe driving is reducing as many distractions as possible and keeping alert behind the wheel."
"That's good advice for all the rest of us who don't ride motorcycles, too," Shafir said.
The paper, "The full moon and motorcycle related mortality: population based double control study," first appeared online Dec. 11 in The BMJ. The project was supported by the Canada Research Chairs Program, the Canadian Institute for Advanced Research, the Canadian Institutes of Health Research, and the Ontario Ministry of Transportation.