The accident happened just before 4:30 p.m. Thursday in the eastbound lanes, just north of the Route 29 Interchange.
Police say an 18-year-old man driving a white Nissan ran out of gas and pulled to the side. His 43-year-old stepfather came over in his pick-up truck to bring him gas. An All-State tow truck driver pulled over and flashed a bright yellow arrow to divert traffic away.
But as the two men were putting gas in the Nissan, a woman in a grayish sedan apparently did not see them in time.
Both the 18-year-old and the stepfather were struck.
A medical helicopter had to land right on the roadway to airlift the stepfather, who was more seriously injured, to an area hospital. At last check, he was undergoing surgery.
Meanwhile, for more than two hours, Route 422 eastbound came to a dead halt, crippling motorists.
"The traffic was horrendous, bumper to bumper. It took forever to get through," said Diane Cleveland of Limerick, Pennsylvania.
"And I had to come out of my house and go the back way all through the avenues in Royersford and come out on Main Street in Royersford and then come over this way," said Lisa D'Annunzio of Royersford, Pennsylvania.
Even a trip from King of Prussia to Radnor proved to be a headache.
"We just had to come all the way through Glasgow, all the way into Phoenixville. it was an hour and a half to get from King of Prussia to here," said David Kempster of Radnor, Pennsylvania.
People tried to find alternate routes.
"Even that traffic there was backed up," said Cleveland, adding there was no escape.
And yet other motorists simply got out of their cars and started talking with each other, knowing full well when something like this happens on Route 422, you're stuck.
All lanes were re-opened just before 8 p.m.