Section 523.10 - Heavy-duty trailers(a) A trailer means a motor vehicle with or without motive power, designed for carrying cargo and for being drawn by another motor vehicle as defined in 49 CFR 571.3 . For the purpose of this part, heavy-duty trailers include only those trailers designed to be drawn by a truck tractor excluding non-box trailers other than flatbed trailer, tanker trailers and container chassis and those that are coupled to vehicles exclusively by pintle hooks or hitches instead of a fifth wheel. Heavy-duty trailers may be divided into different types and categories as follows: (1) Box vans are trailers with enclosed cargo space that is permanently attached to the chassis, with fixed sides, nose, and roof. Tank trailers are not box vans.(2) Box van with front-mounted HVAC systems are refrigerated vans. Note that this includes systems that provide cooling, heating, or both. All other box vans are dry vans.(3) Trailers that are not box vans are non-box trailers. Note that the standards for non-box trailers in 49 CFR 535.5(e)(2) apply only to flatbed trailers, tank trailers, and container chassis.(4) Box van with a length greater than 50 feet are long box vans. Other box vans are short box vans.(5) The following types of equipment are not trailers:(i) Containers that are not permanently mounted on chassis.(ii) Dollies used to connect tandem trailers.(iii) Equipment that serves similar purposes but are not intended to be pulled by a tractor.(b) Heavy-duty trailers do not include trailers excluded in 49 CFR 535.3 .81 FR 74237, Oct. 25, 2016