Police say two vehicles were trying to change lanes, when the driver of a pickup truck made an "unconscionable" decision.
"A man in the red pickup truck pulled out a gun and shot her in the head, killing her," Chester County District Attorney Tom Hogan said.
Bianca Nikol Roberson, an 18-year-old recent high school graduate, was identified as the victim. Authorities say her car veered off the southbound lanes of Route 100 in West Goshen Township and crashed.
The driver of the pick-up truck is described as man in his 30s with a medium build and blonde hair. He's considered armed and extremely dangerous.
Crimestoppers is offering a $5,000 reward in this case.
Anyone who witnessed the incident is urged to contact the West Goshen Police Department Traffic Safety Division at 610-696-7400.
Highway cameras revealed Roberson and the driver of that red pickup truck, possibly a Chevrolet, had some sort of altercation minutes before the situation spun out of control.
"They were jostling for a position or whatever," West Goshen Police Chief Joe Gleason said. "And unfortunately, this gentleman took it to a degree that was just unconscionable."
A second photo shows the red pickup, moments after the crash, fleeing the scene on Route 202 before exiting onto Paoli Pike.
Roberson was a recent graduate of Bayard Rustin High School in West Chester. Her brother said she was "headed for greatness."
"She was a good girl, honor roll student, looking forward to going to college," dad Rodney Roberson said.
Choking back tears, Roberson said Thursday that his 18-year-old daughter's death still hasn't sunk in.
Grief counselors are at Rustin High School on Friday from 9 a.m. to 11 a.m.
This is just the latest tragedy for Roberson's family. Four years ago, they lost Bianca's older brother.
Family members say when Wednesday's crash happened, Roberson had just left an area mall, where she was shopping for college clothes with her mother and grandmother. She was heading to Jacksonville University in Florida in two weeks for orientation, and her goal was to someday solve cases for the FBI.
Her family is hoping someone, particularly the driver, will help close her case.
"If you don't even think it was your fault, and have a conscience, come forward and give us some closure and explain in your own words what happened," Rodney Roberson said.