Bucks County Deputy Coroner John McGhee pronounced Follin dead at the scene. The 8-year-old boy, also from Bristol, was taken to Frankford Hospitals Torresdale Campus for head injuries, according to police.

The tractor-trailer driver, Martin Vera, 41, of Philadelphia, was not injured in the accident, police said.

State police said they don't yet know why the car struck the rear of the trailer and the accident is still under investigation. Follin, Vera and the boy were all wearing seatbelts at the time of the accident, police said. The car came to rest about 20 yards west of the Bristol-Oxford Valley Road underpass. A white sheet covered the driver's side of the car as police and firefighters closed the right lane while they investigated. The tractor-trailer stopped on the shoulder just past the underpass.

Pennsylvania State Police and Edgely Fire Company responded to the accident.

Police said the lane was reopened about 7:23 p.m.

Matt Coughlin can be reached at 215-949-4172 or mcoughlin@phillyBurbs.com