RANDOLPH, Mass. -- A good Samaritan who stopped on an interstate highway to check on a disabled vehicle was killed when his own pickup truck struck him. His daughter, who was riding in his truck with him, was not able to prevent the accident.

State police said Stephen Cullen, 53, of Stoughton, Mass., pulled over onto the breakdown lane on Route 93 North in Randolph early Saturday morning to assist a disabled Ford Explorer.

Cullen got out of his Dodge Dakota and was standing behind it when it began rolling backwards, police said. His daughter Alycia, 23, was a passenger in the Dodge. She tried to stop the truck but was unable to before it hit her father.

"I guess he pulled over to see if they were OK, and he forgot to put his truck in park," his son Stephen Cullen Jr. told The Boston Globe. "It still hasn't sunk in yet."

Cullen was taken to Quincy City Hospital where he was declared dead.

State police Sgt. Robert Bousquet said good Samaritans often are at risk when they stop to help.

"It's a dangerous place to be," Bousquet told the newspaper. "You have 2,000- to 4,000-pound vehicles moving around at extremely high rates of speed...the potential for hazards are great."

Cullen Jr., 20, told the Globe his father was driving to Weymouth to drop Alycia off at a friend's house to see her boyfriend when the accident occurred.