"There's no indication that there was a random shooter," Milligan said. "But right now, we're looking at everything. We're trying to see if there was a reason [the driver] was targeted."
Police will review videotape from the area. They did not disclose what type of weapon was used.
The shooting was near the Montgomery Avenue exit, where Philadelphia police found the Buick stopped in a travel lane. They then alerted state police, who have taken over the investigation.
The car from which the shots were fired had pulled up to the passenger side of El's car, state police said.
Shootings are not unheard of on or near the Schuylkill. But according to Milligan, this was the first in the Montgomery Avenue area since state police started patroling the road in 2007.
In August 1993, Joseph Stanfa was wounded in an assassination attempt on his father, mob boss John Stanfa, near the Vare Avenue exit of the Schuylkill in South Philadelphia. The elder Stanfa, sitting in the front passenger seat of a Cadillac, was not hit. The younger Stanfa, riding in the backseat, survived.
In January 1994, Eileen McGuigan, a 36-year-old mother of four, was killed by a shot fired from another vehicle on the Schuylkill after her fiancé made an obscene gesture to another driver who had cut them off.
In October 2008, a moment of road rage led Christian Squillaciotti to shoot Thomas Timko in the head in front of Timko's young daughter moments after the men passed through the Walt Whitman Bridge tolls. Timko, of Glendora, survived the shooting but was left brain-damaged and unable to work or drive. Squillaciotti, of South Philadelphia, pleaded guilty in May 2010 to the assault.
In September 2005, road rage led to a fatal shooting on the Vine Street Expressway not far from where it merges with the Schuylkill.
Chhona Chher, 20, of Philadelphia, was fatally shot in the chest in a Honda Civic in a westbound lane at Broad Street. Two of Chher's friends had argued earlier with another man driving a Honda Accord. The two cars stopped at Seventh and Vine Streets to settle the dispute, but after the confrontation, the Accord driver followed the Civic and fired at the car.
Although Sunday's shooting happened when traffic wasn't especially heavy, Milligan said he thought there might have been witnesses, perhaps passing motorists unaware a shooting was taking place.
Anyone who was traveling that stretch of the highway, near milepost 341, around 2:50 a.m. Sunday and who saw a vehicle speeding or moving suspiciously is urged to call police at 215-560-6200.
Contact Laura Cofsky at 215-854-2771 or firstname.lastname@example.org.