On Thursday afternoon, he instinctively jumped down to help the man on the tracks, knowing that a train would be arriving any minute.
He called up to people on the platforms to get the trains stopped and held the man's head and neck stable until firefighters arrived. Train traffic was halted.
Southeastern Pennsylvania Transportation Authority spokeswoman Jerri Williams said she spoke with Knafelc soon after his heroics.
"He's clean and sober for about 2½ years but still trying to get his life together," she said. "I think by doing this good Samaritan deed he's kind of surprised himself."
Williams said she saw that as Knafelc recounted the incident on the tracks, "I could see the light go off, the a-ha moment" when he realized that after he was helped by many people in his past, he was able to finally help someone else in return.
"This almost instinctive move to save this guy made him see 'I am a good person,'" Williams said. "It's amazing. This incident may be the start of really good things for him."
Knafelc agreed with that assessment, and he connected the help he's been given by family members to survive his addiction with the favor he did the man on the tracks.
"I'll never be able to repay them, financially or any other way," Knafelc said. "The next best thing I can do is pay it forward."
Investigators do not know what caused the man to fall on the tracks. Surveillance video shows him walking slowly toward the platform's edge and then over it. He was taken to a hospital and listed in stable condition.