a.k.a. Semi Trailer, Tractor Trailer. Generally describes enclosed trailers used to transport materials between locations. Standard lengths for trailers are 45', 48', and 53, with standard internal width of 98" to 99" and internal height of 105" to 110". Refrigerated trailers, also known as "reefers," have smaller internal widths of between 90" and 96" and heights of 96" to 100". Other types of trailers include flatbeds, low boys, and container chassis. Also see Container.