Every state has a maximum legal height for commercial vehicles, measured as the combined height of the trailer and the load.

For example, if a flatbed trailer is 5 feet tall and the cargo is 8 feet 6 inches tall, the total vehicle height is 13 feet 6 inches, which is the legal maximum in many states.

If the combined height reaches 14 feet, the load may still be transported legally in many western states without an overheight permit. However, many eastern states require an overheight permit once the overall height exceeds their legal limit.

Specialized trailers, such as double-drop trailers, allow taller cargo to be transported by lowering the deck height. While these trailers increase the maximum cargo height that can be carried, they are still subject to the same overall legal height restrictions established by each state.