Investigators say a vehicle heading south on Route 1 crossed the median into opposing traffic, colliding with a car merging from Dartmouth Lane.
Troopers say it's unclear why the driver of the first vehicle, 52-year-old Kevin Smith, of Haberson, drove over the median.
Immediately after the initial impact, a third car crashed into the rear of the merging car.
51-year-old Stanley Mutter, of Milford, was driving the merging car. He was first brought by ambulance to Beebe Medical Center, but then was airlifted to Christiana Hospital in critical condition.
The driver and an 11-year-old passenger of the third car were treated for minor injuries at Beebe Medical Center.
Smith was not injured.
Police say charges have not yet been filed.
The northbound side of Route 1 was shut down for more than two hours following the accident.
This material may not be published, broadcast, rewritten, or redistributed.