All trains were running on the inbound tracks because of construction work, Deputy Chief John Livingood of the Abington Township Police said.
"The youth was walking north or in the same direction as outbound trains on what he apparently thought were the inbound only tracks," Livingood said. "He was wearing headphones and apparently listening to music as he walked along the tracks."
The engineer threw the emergency brake and kept blowing the horn but was unable to stop the train before it struck the teen, Livingood said.
The boy was in critical but stable condition at Abington Memorial Hospital.
The Warminster Regional Rail Line was shut down for 10 minutes, and service resumed at 3:20 p.m.
At 3:46 p.m., a 29-year-old Lansdale man was struck by an outbound train near the loading platform at the Lansdale station on the Lansdale/Doylestown line.
Lansdale police responded to the station, at 101 W. Main St., at 3:49 p.m. and found the man under the train conscious and alert, Sgt. Alex Kromdyk said.
Witnesses said the man had scaled a fence separating the SEPTA property from others along Walnut Street and begun walking toward the tracks.
Police said witnesses reported the conductor sounded the train horn but the man never stopped.
As the man began to hoist himself onto the platform, he was struck by the left front of the lead train car and was thrown under the train, which slowed to an emergency stop.
Kromdyk said the man sustained injuries to his head and an ankle but they did not appear to be life-threatening. He was flown to the Hospital of the University of Pennsylvania.
The train line was shut for 45 minutes. Service resumed at 4:30 p.m. No one on the train was hurt, SEPTA spokesman Andrew Busch said.
Neither Williams nor Busch could identify the victims.
"It's just a tragic coincidence," Williams said.
Contact Bonnie L. Cook at 610-313-8232 or firstname.lastname@example.org.