TAMPA — Crashes involving wrong-way driving, like the one that left three people dead Sunday, are occurring in the Tampa Bay area at twice the national rate.

Though Sunday morning's crash may have seemed a horrifying aberration, it is the fourth such accident this year on the same stretch of Interstate 275. Federal and state experts say they are at a loss to explain the spate of wrong-way driving crashes, which fits into a broader and disconcerting picture of the region's traffic problems.

In the Tampa Bay area, wrong-way crashes account for 6 percent of highway crashes, compared with 3 percent nationally.

"Wrong-way crashes are pretty rare," said Florida Department of Transportation spokeswoman Kristen Carson. "But we're having more and more of them in Tampa Bay."

The four accidents on I-275 this year have taken 10 lives, including all of the drivers who went in the wrong direction, leaving no one to explain why they did it.

Florida Highway Patrol troopers say they don't know for certain how Gabrielle Lanier, 33, wound up barreling south on Sunday morning in the northbound lanes of I-275, where she collided with a semitrailer truck. But they suspect Lanier began in the right direction before inexplicably making a U-turn. Lanier, her sister Lakritra Lanier, 31, and their friend, John Pierson, 26, died in the crash. The truck's driver was unharmed.

The Lanier sisters were coming back from a party, said Elcarium Sallye, the father of the youngest of Lakritra's four children. They were on their way to return Pierson to his home in Riverview. Sallye said he did not know if the women had been drinking. A toxicology report for Sunday's accident is pending.

Gabrielle Lanier's driving privileges were suspended three times since 2008, though she had a valid license as of June 25, according to state records. She was driving without insurance, Sallye said.

On Monday, FHP officials released a recording of a 911 call placed moments before Lanier crashed, in which a driver reported seeing a car headed the wrong way just north of Bearss Avenue. A dispatcher told the caller that troopers were being sent to the area.

Across the country, the number of fatalities caused by wrong-way drivers is holding steady, which makes it something of a statistical anomaly, said Federal Highway Administration engineer Jeff Shaw.

Though traffic fatalities are falling overall, dropping to 33,500 in 2013 from a peak of 43,500 in 2005, the number of people dying from wrong-way driving incidents has not changed significantly.

"We've seen the total number of traffic fatalities come down quite a bit, but we haven't seen that translate to wrong-way fatalities," Shaw said. "It's a bit of mystery as to why that's happening."

In Florida, as in some other states, the wrong-way death numbers are increasing, according to statistics compiled by the U.S. Department of Transportation's National Highway Traffic Safety Administration. In 2012, 94 people died in crashes involving a wrong-way driver, up from 75 in 2008.

During that four-year period, a total of 393 deaths were attributed to wrong-way driving in Florida, the third highest in the country. More people died from these crashes in Florida than in California, which has about twice as many residents.

In Tampa, the rash of wrong-way crashes began Feb. 9, when Daniel Lee Morris, 28, got behind the wheel of a friend's Ford Expedition and sped south on I-275's northbound lanes before crashing into a car carrying four University of South Florida students, all of whom were killed.

Two weeks later, 25-year-old Chase Kaleb Leveille of Riverview made a mysterious U-turn, heading north on the interstate's southbound lanes before he plowed head-on into a box truck and was killed.

Then in August, Edward Jose Duran, 23, died when he drove into an ambulance just north of Floribraska Avenue. The ambulance was not carrying any patients and its attendants were hospitalized with minor injuries.

In each case, medical examiners found the drivers had been drinking or using drugs when they got behind the wheel. This is in keeping with national studies that have found that most drivers involved in wrong-way crashes are impaired. A National Transportation Safety Board analysis found that more than 60 percent of wrong-way collisions between 2004 and 2009 were caused by drunken drivers.

Shaw said what's unusual about the recent wrong-way crashes in Tampa is that some of them began with the drivers heading in the right direction before making a U-turn. Most of these crashes happen when people enter the highway in the wrong direction, he said.

To prevent that from happening, FDOT can install wrong-way signs, or signs on the highway alerting vehicles to a wrong-way driver. But there's no clear way to defend against a driver who decides to turn in the opposite direction.

Patrick Mauro, 62, and his wife found themselves in that position last month as they traveled north to meet relatives in Myrtle Beach. They had left early and it was still dark out when they drove along the same stretch of I-275 that had seen three previous wrong-way crashes.

Suddenly, there were headlights coming towards them.

"It was absolute shock," Mauro said. His wife, who was driving, managed to get into the middle lane just before a car flashed by them going in the opposite direction.

"What a way to start a little vacation. It almost ended in tragedy," he said.

Moments later, they passed under an overhead sign flashing. It read: "Wrong way driver, caution."

Times news researcher Natalie Watson and staff writer Jimmy Geurts contributed to this report.