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Two Antioch teenagers are dead and three others are injured after an 18-year-old woman suspected of drunken driving plunged off a highway-interchange flyover in Walnut Creek early Sunday and crashed onto the asphalt below, authorities said.

The driver, in a silver 2000 Honda Civic with four passengers, was headed eastbound on Highway 24 around 4 a.m. Sunday, approaching the Interstate 680 interchange when the crash occurred. The car dropped about 40 to 50 feet, according to the California Highway Patrol.

The CHP described the crash as “tragic.” A relative of the injured driver said the young woman is a recent graduate of an Antioch high school — a good student who was planning to soon head off to college. Now, she and two other young women are hospitalized with major injuries, the CHP said.

#BreakingNews @CHP_GoldenGate @320PIO confirm two people dead, several injured after car driven by teenager careens off 680 flyover in #walnutcreek this AM pic.twitter.com/AHSAr6BYjD — Brian Dinsmore (@BrianKPIX) August 12, 2018

Two 18-year-old Antioch men in the car were declared dead at the scene by emergency personnel. Two 18-year-old women from Antioch and Oakley in the car suffered major injuries and were transported to a hospital, the CHP said.

The driver, Ramya Ramey, from Antioch, also suffered major injuries and was transported to a hospital. Her injuries are not considered life-threatening, the CHP said.

“For reasons unknown that are still under investigation, she allowed the Honda to veer completely off SR-24 and overturned and crashed onto Boulevard Circle, which is below SR-24, causing major damage,” a statement on the Contra Costa CHP Facebook page said.

Speaking by phone on Sunday afternoon, the driver’s relative, Anisha Hackney, said Ramey’s parents are “devastated” by the incident and are sending their prayers to the family of the two teens who were killed in the crash, and to those who were injured.

The CHP statement said Ramey was “placed under arrest for multiple counts of felony manslaughter for killing two of her passengers and multiple counts of felony DUI, causing major injuries to her other passengers.”

Hackney said the family is still waiting for official toxicology reports that would show whether Ramey indeed had alcohol in her system at the time of the crash.

If it is confirmed that was the case, Hackney said it would be an out-of-character decision for Ramey, an honor roll student and recent graduate of Deer Valley High School in Antioch.

“She may have made the wrong decision at the wrong moment, but we’ve all made bad decisions, and some of us have just escaped the negative results that often come along with those bad decisions,” Hackney said.

“That should not color who she is as a person,” Hackney said. “She’s been an upstanding young citizen up to this point. She had goals and dreams and was working towards those goals and dreams right alongside her friends.”

Ramey graduated from Deer Valley in June and was set to attend University of the Pacific in Stockton, where she planned to study biomedical courses, Hackney said.

Ramey was awarded a scholarship from the Woman’s Club of Antioch earlier this year, Hackney said.

“She was making plans to move into her dorm just the other day,” Hackney said.

“It’s been a difficult day, just the gravity of it all” for Ramey’s parents, she said.

Ramey and the other teens in the car were all good friends who hung out together frequently, Hackney said.

“They’ve all known each other for years,” she said.

In 2016, another car veered off this same flyover and crashed through a yoga studio just feet away from where the car Ramey was driving landed Sunday morning. Two people were injured in the 2016 crash, but officials said drugs or alcohol were not a factor in that accident.

The CHP said the investigation into the crash is ongoing. Authorities are asking anyone who witnessed the collision or the events leading up to it to contact Contra Costa CHP in Martinez at 925-646-4980.

Staff writers Judith Prieve and Martha Ross contributed to this article.