A mother and son whose car stalled in the middle of busy Route 309 in Montgomery County were killed when an SUV slammed into their car Monday afternoon.

"They never knew what hit them," said Montgomery County Coroner Walter Hofman.

Pennsylvania State Police said the 2000 Lincoln Town Car broke down in the center lane of the northbound side of Route 309 near the Camp Hill Road overpass in Whitemarsh.

Richard Guerrier, 21, got out of the car to look under the hood while his mother, Esther Louis, 54, went to the back of the car. A Lexus SUV coming around a curve struck and killed them.

"If they'd stayed in the car, they would have survived," Hofman said.

Guerrier, who would have been 22 today, and his mother were from Philadelphia, but police did not release an address.

The driver of the Lexus, Barbara Fellin, 54, of Lower Gwynedd, was airlifted to Abington Memorial Hospital with non-life-threatening injuries.

Contact Kathy Boccella at 610-313-8123 or kboccella@phillynews.com.