Today is the Deadliest Day of the Year for Car Wrecks in the U.S.

It’s not Super Bowl Sunday or even New Year’s Eve that makes for the most lethal day on U.S. highways. It’s Aug. 2.

Thursday is when, on average, car wrecks are likely to kill more Americans than any other day of the year, according to the Insurance Institute for Highway Safety, which based its calculations on fatalities from 2012 to 2016. A total of 505 people were killed on that day during the period.

Since the culprit isn’t icy roads or drunken revelers, what makes that seemingly random date on the calendar so lethal? Sunny skies and vacation travelers, the same reasons the month of August is also one of the deadliest, says Becca Weast, a research scientist at IIHS.

“In the summer, the weather is nice, sunny, and people just are a little more reckless, they’re a little less careful,” Weast said. When the weather is bad or there are other obvious risks that make driving more difficult, “people tend to be a little bit more on guard or more careful,” she said.

August accounted for 15,914 fatalities during the study’s span. The first week of the month is prime vacation time, putting more cars on the road and therefore more chances for an accident. But other than that, “there’s no significant event that makes the first week in August a particular lightning rod for high fatalities,” Weast said.

Other deadly days for drivers (based on deaths occurring between 2012-2016 and data compiled by the IIHS):

July 4

October 25

May 3

November 1

Nationwide Mutual Insurance Co. members reported 60,976 accidents in August 2016, more than in any another month in the last four years, according to the Columbus, Ohio-based company.

Teresa Scharn, associate vice president for product development at Nationwide, agreed that the increase in cars on the road was a contributing factor. Data from the insurer’s SmartRide program, which tracks customers’ driving habits, show there are signals that can predict the likelihood of a crash.

“Some of those are fast acceleration, hard brakes, idle time,” Scharn said. “Those are three really key things that determine whether somebody is potentially more likely to be in an accident.”

SmartRide monitors users’ driving via an app or device installed in the vehicle. Nationwide has 600,000 members and 1.3 million vehicles enrolled in the program. For sharing the data, users receive a 10 percent discount, which can increase to as much as 40 percent based on their driving habits.