Twelve people were killed instantly in Saturday’s collision, which involved a passenger bus, a car and three motorcycles in the Central Java district of Banyumas. Three others died in a hospital.
Local police chief Lt. Col. Dwiyono said the bus was carrying 25 passengers from the Banyumas capital of Purwokerto to Solo town, and hit the four vehicles while trying to overrun another car.
The bus and the four vehicles fell into a five-meter-deep ravine.
It was the worst road accident in Indonesia during the Muslim celebration of Eid-al-Fitr.
National police said 471 people had died in accidents across the country during the annual holiday exodus through Saturday.