A driver uses her phone while sitting in traffic in 2016 in Sacramento. (Rich Pedroncelli/AP)

There are two things to know this holiday season: Distracted driving will increase, and if your smartphone is loaded with apps, they can track just about every move you make.

The confluence of these two seemingly disparate facts is that your phone knows that you are more likely to glance at a text, Facebook or Instagram while behind the wheel during the stretch between Thanksgiving and New Year’s than you might be otherwise.

Why? Nobody can say for sure.

But Matt Fiorentino, director of marketing at TrueMotion, is in a position to speculate. His company, which has a family of driving apps, just released statistics showing a 33 percent holiday jump in distracted driving.

“People travel to see loved ones during the holidays. As they’re driving, they want to provide updates on where they are,” Fiorentino said. “Unfortunately, sometimes they’ll send a text while they’re driving. This also happens when you’re stuck in traffic and want to let your loved ones know you’ll be delayed.”

Fiorentino says people commuting to and from work are less likely to send updates on when they expect to arrive.

The National Safety Council issued a sobering estimate for the long Thanksgiving weekend this year: 433 people would die and an additional 49,400 would be seriously injured in car crashes. The final tally isn’t in for this Thanksgiving, but the NSC says that three years ago, 355 people died on New Year’s Day and 273 on Christmas Day. About a third of those who died had been drinking alcohol.

The tragedy of those statistics makes the TrueMotion projection of a 33 percent increase in distracted driving a cautionary one. The data doesn’t come from a projection or estimate, but rather from the smartphones of 3,000 drivers who had downloaded the TrueMotion app before the survey period between Nov. 18 last year and Jan. 3 this year.

“This is driving data — speeding, braking, distracted driving,” said Emily Goldberg, a colleague of Fiorentino’s at TrueMotion. “We collect driving data using smartphone telematics and analyze it with machine-learning algorithms.”

TrueMotion collected the survey data from its safe-driving app. The app can be downloaded from an app store if the user agrees to abide by TrueMotion’s terms.

“Our technology can go into any mobile app to collect driving data,” Goldberg said.

Fiorentino added via email: “We only use smartphone sensor data to track driving behavior. We never see any content on the phone. So we don’t see emails, Facebook messages, YouTube videos, Candy Crush, etc.”

He said that users opt in to allow their driving to be tracked by the app.

“The TrueMotion Family app enables parents to see how their teens are driving — specifically distracted driving, speeding, and braking,” Fiorentino said. “We do not share TrueMotion Family users’ information with law enforcement or insurers without their prior consent.”

He added, however, that TrueMotion does work with insurance companies.

“Users opt-in to the program to save money on their policy based on how good their driving is,” Fiorentino said. “But users must opt-in to the programs and accept the permissions.”

The company found that active phone use while driving was up 33 percent during the Christmas holiday.

The app also found that people were far more likely to speed during the holiday period. On the average weekday people speed 25 percent of the time, but during the holidays that number jumps to 45 percent.

The good news: While text messages increased, actual phone calls dropped by 45 percent when compared with the average weekday.

How can they gather all these statistics? Can they tell if someone is texting or using Facebook?

“We measure phone behavior with the phone’s sensors,” he said. “Our algorithms can detect tapping and swiping on the phone, when the phone is on and which direction it’s facing, so we can identify when someone is driving distracted.”

How does the app determine if the vehicle is speeding or braking?

“We use the phone’s sensors like accelerometer, gyroscope, magnetometer, and GPS to measure the vehicle’s movement through three-dimensional space,” Fiorentino said. “We compare the speed of the vehicle to the speed limits provided through mapping services. If the vehicle is traveling 10 mph over the posted speed limit, we classify it as speeding. To track braking, we look at the traveling speed and then velocity of deceleration. If the vehicle meets a certain threshold during deceleration, it’s classified as a hard brake.”

How do you tell who is driving and who is a passenger?

“This is a hard problem to solve! We do it by looking at a number of factors,” Fiorentino said. “These include how the person rotates in and out of the car when they enter/exit. If they rotate counterclockwise when entering the car, we know they’re entering from the driver side of the car. We also look at signals such as if they connect to the car’s Bluetooth, put the phone on the windshield (to use maps), and frequent routes. (If you drive from home to your office every day, and you take the same route at the same time on a particular day, the likelihood of you being the driver is high.). . . To differentiate from the front and the back seat of the car, we measure the vibrations of the front and rear axles as the vehicle travels.”

Despite its popularity, text messaging while driving is banned in 47 states. The District and 16 states prohibit handheld cellphone use while driving. The NSC, however, strongly discourages use of hands-free cellphones, too, saying: “Many drivers honestly believe they are making the safe choice by using a hands-free device. But in fact, these technologies distract our brains even long after you’ve used them.”

Your best bet to maintain your privacy and stay safe? Stay off your phone. Period.

The National Highway Traffic Safety Administration says that in 2016, the most recent year for which data is available, 3,450 people were killed and 391,000 injured in crashes involving distracted drivers.

“Everyone wants a holiday to remember, but not for the wrong reasons,” said Deborah A.P. Hersman, a former National Transportation Safety Board chairman who now serves as the NSC’s president. “Let’s keep our holiday gatherings out of the emergency room.”