At least 11 persons were killed on Sunday when a passenger bus plunged into a ravine in Khyber-Pakhtunkhwa province of Pakistan, police said.Many others were injured in the accident near Lowari Top, The News International reported. The injured have been rushed to a hospital.According to the police, the driver of the bus lost control over the vehicle while negotiating a sharp turn in the mountainous terrain.The bus was carrying over 20 persons and was on way from Rawalpindi to Chitral.Traffic accidents frequently happen in Pakistan due to poorly maintained roads, violation of road safety rules and reckless driving.According to Pakistan Bureau of Statistics, over 9,000 road accidents take place every year in the country, killing about 5,000 people.Traffic police officials say 90 per cent of the accidents are caused merely due to human errors.