It happened around 7:00 Sunday morning in the southbound lanes of I-95.
The victim, identified as 30-year-old Vivek V. Siruvuri, was pulled over on the shoulder of the highway to make a repair on his vehicle.
Authorities say once he stepped outside his car, he was struck from behind by an SUV driven by 23-year-old John M. McCool.
Police on the scene say he was thrown about 30 feet onto the highway upon impact.
The victim was taken to Christiana Hospital in serious condition. The driver of the SUV was not harmed.
One lane of the highway was closed for two hours as Hazmat crews cleaned up oil and gasoline from the roadway.
McCool was cited for inattentive driving.
