Jordan Brooks, 15, vaulted across the central reservation of the A63 and was struck by a car driven by a nurse on her way to work at Hull Royal Infirmary on the evening of March 24 last year.
An inquest today heard that another youngster, in a group of teenage boys, had twice put the 3ft motorway cone onto the 50mph flyover on Clive Sullivan Way, at the junction with St Andrew's Quay. The youth, who can't be named, was later prosecuted.
Mum Jenna Brooks said her son "shouldn't have been on the road," but "knew right from wrong" and would have not been "that stupid" as to have been playing chicken.
She said: "He would have got that cone off the road trying to stop someone else getting hurt.
"He put his own life at risk to save a motorist. I'm proud of him for that."
The inquest in Hull heard a collision was "inevitable" with under two seconds passing from the time Jordan jumped into the eastbound carriageway to the impact.
It was dark and the nurse's view was compromised because two of the lights in the centre of the road were out.
In a statement the nurse said she saw a person climbing over the central reservation, and was trying to work out what they were doing, when "all of a sudden there was a huge bang."
"I screamed and stopped the car, the right hand side of the windscreen was shattered and I was showered with glass."
Although distraught and hyperventilating, she told a motorist who came to sit with her and calm her "she was a nurse and should get out and help, but he told me there were others helping."
She was cleared of any blame in the hearing, and the boy's family said they hoped to meet her.
"It might help if she saw us, " said Jordan's grandfather Robert Aubrey. He said the youngster, a junior flyfishing champion, spent much of his time at his house.
He said: "He wasn't frightened of saying 'I love you' when I said 'love you' when it comes to that time of night.
"It just breaks me up - I have done it every night since it happened. It's not easy at all.
"At least we know now he died at the scene - he wouldn't have felt anything, that was Jenna's biggest worry."
Mrs Brooks added: "He was a happy lad, he had everything to live for.
"He had a heart of gold - every single of his friends said that."
The inquest heard that the same boy put the cone out twice. Another boy retrieved it first, before Jordan ran across.
Motorist Matthew Murrell, saw a cone in the middle of the carriageway, and a figure climbing over the barrier, who ran across both lanes, picking up the cone as he ran.
"I had to brake fairly hard to avoid hitting him," he said in a statement. "As he got to the side of the road, he turned and looked straight at me and smiled. I think he was playing chicken."
One of the other boys in the group said the first youngster put it back in the middle of the road a second time.
Toby Craven, who was driving behind the nurse, saw a "dark-coloured figure who seemed to spring over the top of the central reservation in one clean movement."
He said: "It seemed like a flash of light and all sorts of debris seemed to fly up in the air.
"I could see a body that had been launched into the air."
Collision investigator Darrell McPherson said a footprint on the central barrier suggested Jordan, of Caldane, Hull, had vaulted the barrier as a steeplechaser would "entering the carriageway with little reduction in his speed."
The collision, he said, had occurred as a result of Jordan's actions.
Area coroner Rosemary Baxter concluded that Jordan, who suffered extensive head injuries, died as the result of a road traffic collision.