The accident that claimed the 17-year-old's life happened around 12:30 p.m. Saturday on Red Lion Road at Norcom Drive.
Family members say Alvelo's stepfather, 45-year-old Joseph Snyder, had passed out at the wheel.
The teen unbuckled his seatbelt to take the man's foot off the gas and hit the brake. However their pickup truck slammed into a parked paratransit bus nearby.
Three of Alvelo's friends, 18-year-old Nick Pendergrast, 15-year-old Mike Erickson and 16-year-old Dalton Madden, were in the back seat.
All three managed to survive, along with Alvelo's stepfather. Pendergrast said they owe it all to Alvelo.
"He's a hero. He saved my life and everyone else's in that car, because if he didn't take control of the steering wheel we would have hit those trees or a fuel tank that's sitting down there," said Pendergrast at the scene.
Snyder suffered a number of injuries including a broken vertebrae. He remains hospitalized. There was no immediate word what caused him to pass out.
After the crash, Pendergast jumped out of the mangled vehicle and escaped with a sprained wrist. His friends also have a number of injuries, including a broken forearm and sprained ankle.
Erickson and Madden remain at Saint Christopher's Hospital.
At Alvelo's school on Monday, grief counselors and staff arrived early, bracing for the difficult day ahead.
"Our condolences go out to his family. I mean, it's such a hard thing when you lose someone so young," said the school's C.E.O., Paul Stadelberger.
Both Stadelberger and classmates described Alvelo as a personable, outgoing student who always had a smile on his face.
"Whenever you were feeling down or you were upset about something, Chris always found a way to make you happy. He was just that person you could go to in school who would always be there for you. He would help you whenever you needed help. He was just a kind-hearted and helpful person, and we're all going to miss him a lot," said senior Shakiya Lewis
Alvelo was also heavily involved in community service, including the Eagle Scouts.
The accident that claimed his life happened on the way back from a scout service project at Pennypack Park early Saturday afternoon.
Classmates explain he was always thinking of others.
"Chris being the person that he was, that is something that he would do - looking out for everyone else, putting everybody else before himself," said senior Devin Gause.
"I think that's just who he was, to protect other people. Like, he's a hero to all of us," said senior Jared Troutman.
The students' tributes outside school on Monday echoed those given over the weekend. Throughout the day on Sunday, those who knew Alvelo came to the scene of the crash to mourn and pay their respects.
"He would do anything to help anyone out. He would go out of his way to help anyone. He was the most selfless person I've ever met," said Nick Pendergrast.
"It's like a dream. I kind of can't wake up from it, it still hasn't hit me yet just seeing the scene brings everything else back," said Pendergrast.
Alvelo's brother says he was an all-around good teen who wanted to join the military after graduating from New Foundations Charter School.
"Never had to worry about him. Never was a trouble maker, always was a good kid, always got good grades and just a caring kid who never did anything wrong," said Nelson Alvelo.
There was clear evidence of just how much Chris was loved. Throughout Sunday evening, there was a steady stream of classmates and friends who stopped by the scene and a growing memorial.
"There's no other way to put it. He died as a hero, he saved the people he loves, if that's not a hero then what is," said Giovanna Figueroa, classmate.
A candlelight vigil was planned for Monday night in the parking lot of the school.