Graham Manning, 71, had donned an "extremely poor" high-vis jacket just before he was hit by a car on the A35 at Holmsley in the New Forest.
Coroner Grahame Short said Mr Manning had stepped into an unlit road, wearing mostly dark clothing.
He told the hearing in Winchester there had been "room for traffic to pass".
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Mr Manning's partner Pauline Nicholson told the hearing he saw a car veer into a ditch as they were driving home, and pulled over to help.
She said he directed traffic for several minutes before the impact.
"I heard two dull thuds and saw Graham's vest being carried along by a car at roof height," she said.
"As the car braked, the vest - Graham - slipped off the car into a ditch on the other side."
Driver Lucien de-Laloi, whose people carrier hit Mr Manning, said he "stepped from nowhere" into the road in front of him.
A police report said Mr Manning was standing about 0.5m (1.5ft) from the verge when he was hit by Mr de-Laloi's Mitsubishi Space Star at 17:20 GMT on 27 December.
The coroner said Mr de-Laloi, who has not been prosecuted, had been "distracted" by the crash scene on the opposite side of the road.
Mr Manning died "almost instantaneously" from head injuries.
Coroner Mr Short reached a conclusion of death as a result of a road traffic collision.
After the hearing, Ms Nicholson and Mr de-Laloi embraced outside the court room.
A driver was killed when he made a "misguided" decision to pull over and direct traffic at a crash scene, an inquest has heard.