A drop deck flatbed is an open-ended semi-trailer platform with no roof, sides, or doors. It consists of two deck levels.
The height of the trailer is that of a normal flatbed trailer near the tractor unit where it is connected, after which the trailer’s height drops further lower. This drop allows the trailer to haul taller loads than its standard trailer counterpart.
These drop decks are also known as step decks, or lowboy trailers due to their two-level design. ”