The flatbed semi-trailer category includes extendable trailers, skeletal trailers, and container flatbed trailers. This semi-trailer can be used to transport containers. The flatbed trailers have stable structure and lightweight. In order to reduce the weight, this trailer type can be produced as a skeleton type. It includes the gooseneck and ordinary type. The customized flatbed trailer can be used to transport special equipment. Flatbed semi-trailers are mainly used in ports, and a container side loader can be installed on the flatbed to make it easier to unload the container.