The drivers said there were no signs indicating there was construction ahead, so they continued speeding down the dark road before hitting plastic orange barriers and plunging into a hole.
The hole had been dug on Mitttraparp Road in Sung Noen Ma Klua Mai area to lay underground sewage pipes.
Simaporn Khadee driving a sedan and Kittichai Wangklang driving a pick-up truck were immediately rushed to the district hospital.
Eyewitness Thanakrit Apimahacharoenpaisarn told police that he was behind the pick-up truck, but they parted ways when he took the traffic bridge and the pickup drove on.
Thanakrit said he then heard a loud bang, so did a U-turn and returned to find the pick-up in the hole along with a car.
Kittichai said he was heading home and driving at 90 kilometres per hour. He said the road was very dark and there were no signs warning him of a construction site up ahead. By the time he arrived at the spot, it was too late to brake and he ended up hitting the barrier and falling in. He later found that a car was already in the hole.
Kittichai said there were no warning lights at the spot either.