Speed is the probable cause of a crash that killed a young girl and seriously injured her grandmother Wednesday night on the Route 611 Doylestown Bypass.

It happened near the Broad Street Interchange, where a Ford Mustang Cobra hit a Honda CRV Sport-Utility Vehicle in the rear end with enough impact to flip the Honda over several times.

Officials say nine-year-old Holly Huynh  was a passenger in the CRV with her 55-year-old grandmother Suzanne Berry, who was flown to a hospital for treatment.  They are Plumstead Township residents.

Investigators say the Cobra had a supercharger and other parts that made it built for speed.  A witness told police he was doing 75 miles per hour when the Mustang blew past him just before the crash.

Bucks County District Attorney David Heckler says they are doing a very thorough reconstruction and talking to witnesses, and speed appears to have been a significant factor in causing the collision.