The cleaner of the truck died on the spot while the driver and two persons on the motorcycle were seriously injured, police said adding that the injured were rushed to hospital.
The incident occurred on Siwan-Malmalia State Highway near Matuk Chapra village under Siwan Town police station, sources said.
The truck driver tried to swerve the vehicle when he realised that the motorcycle was about to dash against it. As a result, the vehicle lost balance and overturned, sources said.
The truck was coming to Siwan. The dead was yet to be identified.