The accident happened at 11.30pm on the Songkhla-bound Asia highway in Ban Krong E-dam village in Tambon Koh Saba, Thepha district.
Police suspect the car was going at high speed, possibly lost control and hit the rear of the trailer which was on the right lane. The car then rolled over and fell on the road side.
The driver was identified as Nopporn Chuenchoom, 36, while the two passengers have yet to be identified.