The accident happened at around 20 minutes past midnight on Friday on the overpass at the Bang Waek intersection on Ratchapruek Road in Phasi Charone district.
Suchet Chusaeng, 30, a postman at the Bangkok Noi post office, died at the scene, Pol Captain Thawee Boonthan, deputy inspector of the Bang Saothong Police Station, said.
The victim’s face hit the rear bumper of the truck hence his crash helmet failed to save him.
The truck driver, Samarn Saramul, 36, told police that his truck engine broke down while he was returning to Suphan Buri province after delivering construction material to a construction site on Rama IV Road.
He said he had turned on the emergency lights and was trying to fix the engine when the crash occurred within 10 minutes.