A DRIVER whose runaway tractor rolled down a hill and killed an elderly woman has been jailed for 21/2 years for manslaughter. Chang Wai-kwan, 29, was found guilty yesterday by a High Court jury. Mr Justice Wong said everyone licensed to drive a motor vehicle must exercise extreme care and attention. ''There are tens of thousand of cars on the road. If everyone behaved like you there would be more dead bodies in the street than cars,'' he said. ''Licence to drive is not licence to kill,'' added the judge. The evidence clearly showed Chang had completely disregarded the public's safety. Where he parked the huge tractor was unsafe and anyone should have known that without applying the handbrake or engaging the gear, the vehicle would slip down the slope, the judge said. He observed that the woman died through no fault of her own. Chang, who had caused the tragedy due to gross negligence, must be punished and the sentence should also serve as a deterrent. The judge said the way Chang handled the vehicle also showed that he was an incompetent driver and disqualified him from holding or obtaining a driving licence for seven years. Chang did not dispute parking the tractor on the upper slope of Sau Mau Ping Road, but denied the manslaughter of a pedestrian, 62-year-old Kong Wai-kuen. During the trial, Senior Assistant Crown Prosecutor Samuel Leung said the incident occurred at about 8.05 am on August 31 last year. Shortly after Chang left the tractor, it rolled down the hill, knocked into a railing and hit Kong. Chang's counsel, Joe Kenny, asked the court to view the case as one of reckless driving causing death. It was an isolated incident and since then Chang had stopped driving a tractor and now worked as a clerk, he said. The knowledge that he caused the death of Kong would stay with him for the rest of his life.