Police said driver Somjit Khemthong, 55, and passenger Surapol Chantha, 39, died in the 3.30am accident on Malai Man Road in Moo 3, Tambon Thung Khok, Song Phi Nong district.
Both worked for a rescue foundation in Ratchaburi.
Police believe the driver was speeding and might have fallen asleep at the wheel.