"The truck lost control and smashed into a car in front as well as an oncoming bus," said Lieutenant Colonel Patipan Mahatthanavisan in Tak province.
A spokesperson for the Tak provincial hospital said 14 people died in the accident, which happened near the site of a previous bus crash in March in which 30 people were killed.
Thailand's roads are among the world's deadliest and accidents are common.
A recent report by the World Health Organization said Thailand saw 38.1 road deaths per 100,000 people in 2010 -- behind only the Dominican Republic in the Caribbean and the South Pacific island of Niue.